A253254 Largest prime factor of the n-th 11-gonal number.

11, 5, 29, 19, 47, 7, 13, 37, 83, 23, 101, 13, 17, 5, 137, 73, 31, 41, 173, 13, 191, 23, 19, 109, 227, 59, 7, 127, 263, 31, 281, 29, 23, 11, 317, 163, 67, 43, 353, 181, 53, 43, 389, 199, 37, 47, 17, 31, 443, 113, 461, 53, 479, 61, 71, 23, 103, 131, 41, 271, 31, 7, 569, 17, 587, 149, 17, 307, 89, 79

Offset: 2

Author

Gionata Neri, May 31 2015

Keywords

• nonn

Comments

a(A024907(n)) = A061238(n).

Links

• Robert Israel, Table of n, a(n) for n = 2..10000

Crossrefs

Cf. A006530, A051682, A069902 (similar, with triangular numbers).

Programs

Maple

gpf:= n -> max(numtheory:-factorset(n));
seq(gpf(n*(9*n-7)/2),n=2..100); # Robert Israel, Jun 24 2015

PARI

a(n) = my(f = factor(n*(9*n-7)/2)); f[#f~,1]; \\ Michel Marcus, May 31 2015

Formula

a(n) = A006530(A051682(n)).