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

Author

Clark Kimberling

Keywords

• nonn

Links

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

Crossrefs

Cf. A006530, A023515, A023525.

Programs

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

Extensions

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