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 A191546 Smallest prime factor of prime(n)^n + 1 having the form 2*k*n+1. 2
 3, 5, 7, 1201, 13421, 28393, 22796593, 15073, 163, 421, 757241, 3512477579761, 79, 29, 24317675453761, 136593761, 21199857783625129028395239857, 37, 2494605276120959, 41, 43, 89, 691, 97, 488700001, 53, 17713, 4201, 59, 181, 2729, 449, 67, 137, 71 (list; graph; refs; listen; history; text; internal format)
 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 Cf. A069463 (Greatest prime factor of prime(n)^n+1). Sequence in context: A068832 A046472 A065824 * A069463 A288212 A273010 Adjacent sequences:  A191543 A191544 A191545 * A191547 A191548 A191549 KEYWORD nonn AUTHOR Michel Lagneau, Jun 05 2011 STATUS approved

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Last modified April 7 13:55 EDT 2020. Contains 333305 sequences. (Running on oeis4.)