TherewasonceavictimofoverwhelmingnumberscalledKingShirhamofIndia,who,accordingtotheoldlegend,wantedtorewardhisgrandPrimeMinisterSissaforinventingandpresentingtohimthegameofchess.Thedesireofthecleverministerseemedverymodest.“Majesty,”hesaidkneelinginfrontoftheking,“givemeagrainofwheattoputonthefirstsquareofthischessboard,andtwograinstoputonthesecondsquare,andfourgrainstoputonthethird.Andso,ohKing,doublingthenumberforeachsucceedingsquare,givemeenoughgrainstocoverall64squareoftheboard.”“Youdonotaskformuch,ohmyfaithfulservant,”exclaimedtheking,secretlyenjoyingthethoughtthathisliberalproposalofagifttotheinventorwouldnotcosthimmuchofhistreasure.“Yourwishwillcertainlybegranted.”
Andheorderedabagofwheattobebroughttothethrone.Butwhenthecountingbegan,itwasfoundthatthebagwasemptiedbeforethetwentiethsquarewasaccountedfor.MorebagsofwheatwerebroughtbeforethekingbutthenumberofgrainsneededforeachsucceedingsquareincreasedsorapidlythatitsoonbecameclearthatwithallthecropofIndianthekingcouldnotfulfillhispromisetoSissa.Todosowouldhaverequired18,446,744,073,709,551,615grains!Assumingthatabushelofwheatcontainsabout5milliongrains,onewouldneedsome4×1012bushelstosatisfythedemandofSissa.
Sincetheworldproductionofwheataveragesabout2×109bushelsayear,theamountrequestedbytheministerwasthatoftheworld’swheatproductionfortheperiodofsometwothousandyears!ThusKingShirhamfoundhimselfdeepindebttohisministerandhadeithertofacetheincessantflowofthelatter’sdemands,ortocuthisheadoff.Wesuspectthathechosethelatteralternative.