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

2,1

Comments

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

Links

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

Formula

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

Maple

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

Prog

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

Crossrefs

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

Sequence in context: A127820 A168206 A120831 * A363347 A229525 A174103

Adjacent sequences: A253251 A253252 A253253 * A253255 A253256 A253257

Keyword

nonn

Author

Gionata Neri, May 31 2015

Status

approved