A023517 Greatest prime divisor of prime(n)*prime(n-1) - 1.

5, 7, 17, 19, 71, 11, 23, 109, 37, 449, 191, 379, 881, 101, 83, 521, 257, 227, 41, 2591, 31, 149, 1231, 83, 79, 743, 29, 17, 3079, 41, 4159, 997, 9521, 109, 1607, 439, 853, 1361, 107, 397, 167, 3457, 2633, 1901, 1153, 3499, 1307, 2531, 79, 13339, 9281, 929

Offset

2,1

Links

Hugo Pfoertner, Table of n, a(n) for n = 2..10000

Prog

(PARI) gpf(x) = {my (f=factor(x)); f[#f[, 2], 1]};
a023517(pmax) = {my(pp=2); forprime (p=3, pmax, print1(gpf(pp*p-1), ", "); pp=p)};
a023517(300) \\ Hugo Pfoertner, Oct 09 2022

Crossrefs

Cf. A006530, A023515, A023525.

Sequence in context: A242929 A128490 A023519 * A128491 A146949 A048700

Adjacent sequences: A023514 A023515 A023516 * A023518 A023519 A023520

Keyword

nonn

Author

Clark Kimberling

Extensions

a(1)=2 removed by Sean A. Irvine, Jun 05 2019

Status

approved