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A262812 Values of n such that sigma(n!) mod sigma(n) is not 0. 1
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 (list; graph; refs; listen; history; text; internal format)
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
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
Sequence in context: A111206 A087112 A077554 * A287296 A275197 A118778
KEYWORD
nonn
AUTHOR
Altug Alkan, Oct 03 2015
STATUS
approved

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Last modified March 28 14:38 EDT 2024. Contains 371254 sequences. (Running on oeis4.)