OFFSET
1,1
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..82
EXAMPLE
a(4) = 1201 because prime(4)^4 + 1 = 7^4+1 = 2402 = 2*1201; the prime divisor of the form 2kn + 1 is 1201 = 2*150*4 + 1 with k = 150.
MAPLE
A191546 := proc(n) local ifs, twkn ; ifs := sort(convert(numtheory[factorset]( 1+ithprime(n)^n), list)) ; for twkn in ifs do if (twkn-1) mod (2*n) = 0 then return twkn; end if; end do: return -1 ; end proc: # R. J. Mathar, Jun 18 2011
MATHEMATICA
Table[p = First /@ FactorInteger[Prime[n]^n + 1]; Select[p, Mod[#1, n] ==
1 &, 1][[1]], {n, 1, 35}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Michel Lagneau, Jun 05 2011
STATUS
approved