Why doesn't my Fibonacci number with BigInteger that is 50000th number does not match with this website?

Question

My Fibonacci Number Sequence Generator is something like below:

import java.math.BigInteger;

public class FibonacciGerenrate {
    public static void FibonacciGenSerial(int n) {
        BigInteger bgIntX = BigInteger.valueOf(0L);
        BigInteger bgIntY = BigInteger.valueOf(1L);
        BigInteger bgSwap = BigInteger.valueOf(0L);
        BigInteger bgSwap2 = BigInteger.valueOf(0L);
        for (long i = 0; i < n; ++i) {
            if (i == 0) {
                System.out.println(bgIntX);
            }
            if (i == 1) {
                System.out.println(bgIntY);
            }
            if (i > 1) {
                bgSwap = bgIntY;
                //bgSwap2 = bgIntX;
                bgSwap2 = bgSwap.add(bgIntX);
                System.out.println(bgSwap2);
                bgIntX = bgIntY;
                bgIntY = bgSwap2;
            }
        }
    }
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        FibonacciGenSerial(50000);
    }
}

But after two minutes the result of my 50000th Fibonacci number is given below. And it doesn't match with the output result of the following website. Why is that? Am I wrong? How can I fix it?

66610064856548120501095154756075093343195047993708099477375141547532964735744982057405586910135453317984257173051850425269005830903016595779361189318480460432263495069730831549328522582752196808116762887245276861573810893922487614112332131447327026946500069765187768832277257729618708926671727184624303234271016946300753690089694872668234747039672222754542282809799056369778982887962146006571530973385585931580225071548761581650961729045046999773643069047328836799163834287241494009774822393284062050442866852092165534443030122421569289771029461808394129839470800968189941922823095945892914724270290558786093081606764119502294557343225831050145740615845398538754099667551857081505145914192371986853474829030772939997481679950787798241405730044738423657870813686922001808204020497927863984410475799450102024307635126674812880589349348338816849076984995221680565701087482109051429640635511055385362029365531396480686992966236591223240748679048229021441905273747815610237112260112626971693396914285142492837605024347972376382682529071928865066892554191083547871909075328203091593685366000104209011205655103765692163314489320649053274472398039106034401210510904148546373577817869597234641984204136081606965376081671760214845672283364302380249632455169706097689385559790516703732515320628936714829619473520244891182635156903864283637327338843874922050683809757164290322560919737434673032512829854173010086866283640837065288468328563450565264055397838363874768761698040472871606132845264830299898205481290324873790250850474814796601361448699345926865385396866175509111011283683190451816250247900309392607624110383274686477950332461287023842565553531075303176842414038672707462126821101192336155458263767255576329676676385435189241379727728606036145811998728296795168424187332546571661526128631703999189154473171320514908389565012076494856414350467577474273078193192844957539025686673815027550418919507953650259239244864250462564522297662525715939931499962332419762679510332171832458076138703791418928563998232741921141727197507150961277771493837880987115837735703353503884191924924808646704340969313813711259501469283427071150001013850652434969007194639344964809920871446368709036686494541133624694266350978978107988901996726878935786907464333157497368648145022365338982246052018355810596322374660521799722238788975138350998808258094462046436616361067982591638692789229509537480119197409643634026773443373025129931338996241399320186340308384153868634816062107376757805792606201297506541364000660069310378054902890586457488600567896639285469354123073089981194599514238915327024035410099941143701882886885940025296761321172627644655173778938074213193122783965718198811886583348081615138910810552853721640396462508702898682052022871501068500759185661451477874089305741895756703848368707196681251984148914607125386988942305070956759661079971986703677076142374480093014444671998584563907194861154951416777474099090913906032758708770706716510590351851201500846147801507116561269302712116615467344480523151477764204278602687955720471934033159113684440379149915392240208632580581913462346462169595980609650391881360101444448149790600044818965830414353121162355307984491705498308299877695083600909545331803065929636374298012074382265879893444966837920641517460750609376218225411061568156971708321149411401877225009767672594115777917493273482056841422636330423796843684224807582328296354387110563820291694527781476886435491676062102877902953870557828292581657909377223128871601370819443443839414915149119557260331485401284014960639838226962551714777113705231188336279784205334400527059485415970629537379730263235662942127608151788601979003265802695661079894975212910780592945880102717947557180961111174075876337315347618080048750360060625374033120165172161405862339297220270952928169087676191742275936432001585742739127040633107887843930535666532434497492496608869154685340157351077611921363288723681485533785281509553023095292732955637467133180314835224325126328326512861426183604514729431981968847138832696941757990475746492270805362894515022333557855175908119469598287679001166982526351870413354309571905129871460657994112839210151343482792039124227708102509435955128831798889370953478197839394511709720707672479149461613883729898125494050784317670102724828599302386049375003047554596763721509233075791452705168253523857887416941641934382681327667931787399847247174968667576531493401755944688391442851056272286443343949814649512011991390134623807794172800284910823573977363026741805564758736377650448602867543112950954505940308945594651909195925730158067567345829621436910581500471111570556873207847296213830678877271870212276670148820316719450246004679777236884411767853700029638436700329837185680974391498701152047035645035307499132568161461798404991288961905874634150213334951055696539282402734442460645370737708072984340255015144416044324020543447986898160999258594457203578619548589953286076338433725625036151809848085023119743950100664168691919815663996294970414903921833292899967980575000130822927943670996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37172930233933594485324619433561564931911914888793630226393645387832882895644605397261496725355227817783507292619445421611950535223331719341500756971803362136404519452880893229885903007294748984670394618952806821098740393146788700124820764553041872496073332651308037095119882100202710186702753433978399149908454238724269918322749507909772992037226532802201150761626111638906545107602875995114792979876216193958825864398145879704552311475748837637501

But this Fibonacci generator website outputs a different result: 50000th Fibonacci number by this website

Does this answer your question? [Fibonacci calculator with BigIntegers](https://stackoverflow.com/questions/29617340/fibonacci-calculator-with-bigintegers) — Harshal Parekh, May 13 '20 at 17:59
Is it a simple off-by-one error? Have you checked the first 20(?) numbers to see if the algorithm is correct? — Progman, May 13 '20 at 18:01
Does your algorithm show that the 5th Fibonacci number is 5? — David Conrad, May 13 '20 at 18:03
Your program shows the first Fibonacci number as 0, which is wrong. — David Conrad, May 13 '20 at 18:05
First of all I am not using recursion. So sorry that posting doesn't answer my question. Extremely sorry. Second it's classical Fibonacci sequence which starts from 0 then 1.... — , May 13 '20 at 18:14
@mvr950 According to [Wikipedia](https://en.wikipedia.org/wiki/Fibonacci_number), Fibonacci(0) is 0, Fibonacci(1) is 1, Fibonacci(2) is 1, etc. So the Fibonacci(50000) is the one starting with 10777734893, and the one you found is Fibonacci(49999). Therefore it's your definition that's incorrect. — Olivier Grégoire, May 13 '20 at 18:26
@OlivierGrégoire Thank you for clearing that up. Now I understand. — , May 13 '20 at 18:38

score 1 · Accepted Answer · edited May 20 '20 at 18:25

Here we go:

public class FibonacciGerenrate {
    public static void FibonacciGenSerial(int n) {
        BigInteger bgIntX = BigInteger.valueOf(1L);
        BigInteger bgIntY = BigInteger.valueOf(1L);
        BigInteger result = BigInteger.valueOf(0L);
        for (long i = 0; i < n; i++) {
            if (i == 1) {
                System.out.println(bgIntX);
            }
            if (i == 2) {
                System.out.println(bgIntY);
            }
            if (i > 2) {
                result = bgIntY;
                result = result.add(bgIntX);
                System.out.println("result: " + result);
                bgIntX = bgIntY;
                bgIntY = result;
            }
        }
    }
    public static void main(String[] args) {
        FibonacciGenSerial(50000);
    }

as the others already stated Fibonacci's sequence start from 1 not 0 . So basically, with your code you are getting the 49'999th Fibonacci's number. I also improved your code to be a bit faster. No need for 2 swap fields.

score 0 · Answer 2 · answered May 13 '20 at 18:07

0

Your number matches the 49999th number of the Fibonacci generator website you linked. So i guess you have to do a little change in your for loop and add 1 iteration:

Change for(long i = 0; i < n;++i) { to for(long i = 0; i <= n;++i) {

answered May 13 '20 at 18:07

sapisch

535
3
14

WJS · Answer 3 · 2020-05-13T20:59:33.483

You can avoid the 1 and 2 conditionals by simply printing out fib from the start, and then doing the swap.

Or you can just print 0 and 1 and then start the loop at i = 2, ensuring that you update the running series appropriately.

BigInteger start = BigInteger.ZERO;
BigInteger next = BigInteger.ONE;
BigInteger fib = start;
for (int i = 0; i < 10; i++) {
    System.out.println(fib);
    fib = start.add(next);
    next = start;
    start = fib;
}

Prints

Why doesn't my Fibonacci number with BigInteger that is 50000th number does not match with this website?

3 Answers3