A250205 Riesel problem in base 6: Least k > 0 such that n*6^k-1 is prime, or 0 if no such k exists.
1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 0, 1, 2, 1, 1, 0, 1, 1, 1, 2, 0, 1, 1, 2, 1, 0, 2, 1, 1, 1, 0, 1, 1, 2, 2, 0, 4, 1, 1, 1, 0, 1, 1, 1, 1, 0, 1, 4, 1, 3, 0, 1, 1, 6, 2, 0, 5, 1, 1, 1, 0, 6, 2, 1, 1, 0, 1, 2, 10, 1, 0, 1, 3, 1, 1, 0, 1, 1, 2, 1, 0, 1, 8, 1, 1, 0, 1, 2, 2, 4, 0, 49, 1, 1, 1, 0, 2, 1, 1, 1, 0, 2, 1, 6, 2, 0, 1, 1, 1, 1, 0, 5, 1, 1, 2, 0, 1, 10, 2, 1
Offset: 1
Keywords
Links
- Eric Chen, Table of n, a(n) for n = 1..1000
- Gary Barnes, Riesel conjectures and proofs
Crossrefs
Programs
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Maple
N:= 1000: # to get a(1) to a(N), using k up to 10000 a[1]:= 1: for n from 2 to N do if n mod 5 = 1 then a[n]:= 0 else for k from 1 to 10000 do if isprime(n*6^k-1) then a[n]:= k; break fi od fi od: seq(a[n],n=1..N); # Robert Israel, Mar 17 2015 -
Mathematica
(* m <= 10000 is sufficient up to n = 1000 *) a[n_] := For[k = 1, k <= 10000, k++, If[PrimeQ[n*6^k - 1], Return[k]]] /. Null -> 0; Table[a[n], {n, 1, 120}] -
PARI
a(n) = if(n%5==1 && n>1, 0, for(k = 1, 10000, if(ispseudoprime(n*6^k-1), return(k))))
Formula
a(A024898(n)) = 1. - Michel Marcus, Mar 16 2015
Comments