A275630 a(n) = product of distinct primes dividing prime(n)^2 - 1.

3, 2, 6, 6, 30, 42, 6, 30, 66, 210, 30, 114, 210, 462, 138, 78, 870, 930, 1122, 210, 222, 390, 1722, 330, 42, 510, 1326, 318, 330, 798, 42, 4290, 2346, 4830, 1110, 570, 6162, 246, 3486, 7482, 2670, 2730, 570, 582, 462, 330, 11130, 1554, 12882, 13110, 2262, 3570, 330, 210, 258, 8646, 2010

Offset: 1

Author

N. J. A. Sloane, Aug 07 2016

Keywords

• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Subsequence of A007947.

Cf. A077063, A077066, A084920.

Programs

Mathematica

a[n_] := Times @@ FactorInteger[Prime[n]^2 - 1][[;; , 1]]; Array[a, 60] (* Amiram Eldar, Jan 30 2021 *)

PARI

a(n) = factorback(factorint(prime(n)^2-1)[, 1]); \\ Michel Marcus, Jan 30 2021

Formula

a(n) = A007947(A084920(n)). - Michel Marcus, Jan 30 2021

a(n) = A077063(n)*A077066(n)/2, for n > 1. - Amiram Eldar, Jan 30 2021