A274552 Numbers k such that sigma(k) == 0 (mod k-3).

2, 4, 5, 6, 7, 8, 15, 52, 315, 592, 1155, 2102272, 815634435

Offset: 1

Author

Paolo P. Lava, Jun 28 2016

Keywords

• nonn
• more

Examples

			sigma(4) mod (4-3) = 7 mod 1 = 0.
		

Crossrefs

Contains subsequence A141548.

Cf. A000203, A067702, A087485, A274551, A274553, A274554, A274556, A274557, A274558, A274559, A274560, A274561, A274562, A274563, A274564, A274565, A274566.

Programs

Magma

[n: n in [1..2*10^6] | n ne 3 and SumOfDivisors(n) mod (n-3) eq 0 ]; // Vincenzo Librandi, Jul 02 2016

Mathematica

k = -3; Select[Range[1, 10^6], # + k != 0 && Mod[DivisorSigma[1, #], # + k] == 0 &] (* Michael De Vlieger, Jul 01 2016 *)

PARI

is(n) = if(n == 3, return(0), Mod(sigma(n), n-3)==0) \\ Felix Fröhlich, Jul 02 2016

Extensions

a(12)-a(13) from Giovanni Resta

a(1)=2 inserted by Max Alekseyev, Jun 08 2025