A262812 Values of n such that sigma(n!) mod sigma(n) is not 0.

4, 6, 9, 10, 16, 25, 45, 48, 50, 64, 86, 122, 192, 256, 289, 314, 326, 448, 562, 578, 706, 722, 729, 794, 842, 1226, 1346, 1458, 1514, 1681, 1754, 1922, 2186, 2401, 2566, 2601, 2916, 3362, 3481, 3866, 3986, 4046, 4096, 4274, 4852, 5043, 5186, 5414

Offset

1,1

Comments

Subsequence of A002808.

Motivation was the investigation of sum of divisors of n! in terms of sum of divisors of n.

Obviously, a(n) cannot be a prime number, although it can be a semiprime number.

Is this sequence infinite?

Links

Table of n, a(n) for n=1..48.

Formula

A066247(a(n)) = 1.

A000005(a(n)) > 2.

A001222(a(n)) > 1.

Example

a(1) = 4 because sigma(4!) mod sigma(4) = 60 mod 7 = 4.
a(2) = 6 because sigma(6!) mod sigma(6) = 2418 mod 12 = 6.
a(3) = 9 because sigma(9!) mod sigma(9) = 1481040 mod 13 = 2.

Prog

(PARI) for(n=1, 1e30, if( sigma(n!) % sigma(n) != 0 , print1(n", ")))

Crossrefs

Cf. A062569, A000203.

Sequence in context: A111206 A087112 A077554 * A287296 A275197 A118778

Adjacent sequences: A262809 A262810 A262811 * A262813 A262814 A262815

Keyword

nonn

Author

Altug Alkan, Oct 03 2015

Status

approved