A113930 Numbers k such that sigma(k) and phi(k) are both triangular numbers.

1, 2, 22, 3051, 3219, 3393, 5057, 8653, 75618, 95675, 100503, 102949, 104714, 287826, 438547, 522339, 537159, 688050, 2191200, 2317118, 2418548, 2507683, 2599128, 3212964, 4534573, 5367797, 6047913, 6302639, 7689149, 13758296, 14380145, 15342050, 16148979

Offset

1,2

Comments

phi(k) = A000010(k) is the Euler totient function, while sigma(k) = A000203(k) is the sum of divisors of k.

Links

Donovan Johnson, Table of n, a(n) for n = 1..207 (terms < 10^12)

Example

sigma(100503) = 156520 = T(559) and phi(100503) = 61776 = T(351).

Prog

(PARI) isok(n) = ispolygonal(sigma(n), 3) && ispolygonal(eulerphi(n), 3); \\ Michel Marcus, Jan 26 2014

Crossrefs

Cf. A000010, A000203, A000217.

Subsequence of A045746.

Sequence in context: A182293 A222000 A261400 * A181235 A387042 A246852

Adjacent sequences: A113927 A113928 A113929 * A113931 A113932 A113933

Keyword

nonn

Author

Giovanni Resta, Jan 30 2006

Status

approved