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Search: id:A139023
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| A139023 |
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Smallest prime factor of n! + 2^n - 1. |
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+0
7
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| 2, 5, 13, 3, 151, 3, 5167, 3, 7, 3, 39918847, 3, 17, 3, 7, 3, 829, 3, 25561, 3, 7, 3, 929, 3, 67, 3, 7, 3, 37, 3, 941, 3, 7, 3, 31, 3, 47, 3, 7, 3, 839, 3, 167, 3, 7, 3, 101, 3, 859, 3, 7, 3, 165437, 3, 23, 3, 7, 3, 199, 3, 526588200926847656291, 3, 7, 3, 31, 3, 157, 3, 7, 3
(list; graph; listen)
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OFFSET
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1,1
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REFERENCES
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F. Luca and I. E. Shparlinsky, 2005. On the largest prime factor of n! + 2n - 1. J. Th. des Nombres de Bordeaux Vol.17, Fasc. 3
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LINKS
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K. Brockhaus, Table of n, a(n) for n = 1..108.
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MATHEMATICA
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a = {}; Do[AppendTo[a, n! + 2^n - 1], {n, 1, 40}]; b = {}; Do[c = FactorInteger[a[[n]]]; d = c[[1]]; AppendTo[b, d[[1]]], {n, 1, Length[a]}]; b
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PROGRAM
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(MAGMA) trialdiv:=function(n, P) val:=0; for p in P do if n mod p eq 0 then val:=p; break; end if; end for; return val; end function; P:=PrimesUpTo(300000000); [ trialdiv(a, P) where a is Factorial(n)+2^n-1: n in [1..70] ]; //a(61) requires a separate computation. [From Klaus Brockhaus (klaus-brockhaus(AT)t-online.de), Nov 06 2009]
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CROSSREFS
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Cf. A127986, A127987, A139024.
Sequence in context: A135329 A114508 A164793 this_sequence A166134 A067365 A112838
Adjacent sequences: A139020 A139021 A139022 this_sequence A139024 A139025 A139026
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KEYWORD
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nonn,new
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AUTHOR
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Artur Jasinski (grafix(AT)csl.pl), Apr 06 2008, corrected Apr 22 2008
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EXTENSIONS
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a(1) - a(40) verified and a(41) - a(70) added by Klaus Brockhaus (klaus-brockhaus(AT)t-online.de), Nov 06 2009
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