A175875 Numbers k such that sigma(k+3) = 3*sigma(k).

3, 30237, 292317, 3116957, 4044037, 6902277, 73442597, 115767957, 137410557, 416776357, 526908197, 541579497, 695350653, 758403357, 1105731897, 1178082357, 1233277917, 1309742557, 1866261597, 1998267037, 2161411557, 2563416237, 2750761437, 2873771997, 2892203997, 3331848517, 3621735037, 3758847117

Offset: 1

Author

Zak Seidov, Oct 06 2010

Keywords

• nonn

Comments

a(1) = A175874(3).

Links

• Giovanni Resta, Table of n, a(n) for n = 1..180 (terms < 10^12)

Crossrefs

Cf. A000203, A002961, A175874, A272027 (3*sigma(n)).

Programs

Magma

[n: n in [1..10^8] | SumOfDivisors(n+3) eq 3*SumOfDivisors(n)]; // Vincenzo Librandi, Jul 28 2017

PARI

isok(n) = sigma(n+3) == 3*sigma(n); \\ Michel Marcus, Oct 19 2013

Extensions

a(8)-a(21) from Donovan Johnson, Oct 11 2010

a(22)-a(24) from Donovan Johnson, Sep 10 2012

a(25) from Zak Seidov, Jul 07 2013

a(26)-a(28) from Chai Wah Wu, Jul 27 2017