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

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

Offset

1,1

Links

Table of n, a(n) for n=1..12.

Example

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

Maple

with(numtheory); P:=proc(q, h) local n;  for n from 1 to q do
if n+h>0 then if type(sigma(n)/(n+h), integer) then print(n); fi; fi; od; end: P(10^9, -3);

Mathematica

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

Prog

(Magma) [n: n in [4..2*10^6] | SumOfDivisors(n) mod (n-3) eq 0 ]; // Vincenzo Librandi, Jul 02 2016
(PARI) is(n) = if(n < 4, return(0), Mod(sigma(n), n-3)==0) \\ Felix Fröhlich, Jul 02 2016

Crossrefs

Cf. A000203, A067702, A087485, A141548, A274551, A274553-A274566.

Sequence in context: A059709 A344580 A071623 * A280682 A140293 A075341

Adjacent sequences: A274549 A274550 A274551 * A274553 A274554 A274555

Keyword

nonn,more

Author

Paolo P. Lava, Jun 28 2016

Extensions

a(11)-a(12) from Giovanni Resta

Status

approved