A271322 Largest prime factor of the n-th n-gonal number (A060354).

2, 3, 2, 7, 11, 7, 11, 29, 37, 23, 7, 67, 79, 23, 53, 17, 137, 19, 43, 191, 211, 29, 127, 277, 43, 163, 11, 379, 37, 109, 233, 71, 23, 281, 149, 631, 29, 13, 53, 71, 821, 431, 113, 947, 991, 47, 541, 1129, 107, 613, 29, 1327, 197, 179, 743, 67, 1597, 827

Offset: 2

Author

Colin Barker, Apr 04 2016

Keywords

• nonn

Examples

			a(5) = 7 because A060354(5) = 35 = 5 * 7.
		

Links

• Colin Barker, Table of n, a(n) for n = 2..1000

Crossrefs

Cf. A006530, A060354, A271319, A271320, A271321.

Programs

PARI

pg(m, n) = (n^2*(m-2)-n*(m-4))/2 \\ n-th m-gonal number
lpf(m) = vecmax(factorint(m)[, 1]) \\ Largest prime factor
a(n) = lpf(pg(n, n))
vector(100, n, n++; a(n))

Formula

a(n) = A006530(A060354(n)).