A046840 Number of divisors divides sum of 4th powers of divisors.

1, 3, 4, 5, 7, 11, 12, 13, 15, 16, 17, 19, 20, 21, 23, 25, 27, 28, 29, 31, 33, 35, 37, 39, 41, 43, 44, 47, 48, 49, 51, 52, 53, 55, 57, 59, 60, 61, 65, 67, 68, 69, 71, 73, 75, 76, 77, 79, 80, 81, 83, 84, 85, 87, 89, 91, 92, 93, 95, 97, 100, 101, 103, 105, 107, 108, 109, 111

Offset

1,2

Comments

A020486 is very similar to this sequence, but it does not include the following values below 1000 (which this sequence does include): {16, 80, 81, 176, 304, 324, 400, 405, 464, 496, 656, 784, 880, 891, 944, 976}.

Links

T. D. Noe, Table of n, a(n) for n = 1..1000

Example

x=16 with 5 divisors, sigma(k,16) = 5, 31, 341, 46801, 69905 for k=0,1,2,3,4, respectively. It is seen that sigma(4,16) = 13981*sigma(0,64) = 41*sigma(2,64)*sigma(0,64).

Prog

(Magma) [n: n in [1..120] | IsZero(DivisorSigma(4, n) mod NumberOfDivisors(n))]; // Bruno Berselli, Apr 11 2013
(PARI) isok(n) = sigma(n, 4) % numdiv(n) == 0; \\ Michel Marcus, May 13 2018

Crossrefs

Cf. A020486, A003601.

Sequence in context: A022440 A347805 A088130 * A057773 A020486 A091428

Adjacent sequences: A046837 A046838 A046839 * A046841 A046842 A046843

Keyword

nonn

Author

Labos Elemer

Status

approved