A076230 Numbers k such that sigma_2(k)/k and sigma_4(k)/k are integers.
1, 84, 435708, 986076, 1441188, 6066396, 7407036, 16763292, 18735444, 78863148, 260855028, 318502548, 1340673516, 3391115364, 10829086632, 45076171140, 45582899544, 57648961188, 77314641768, 128293717860, 149098104540, 174975241896, 440359518060, 461191689504
Offset: 1
Keywords
Examples
For k = 6066396, sigma_2(k)/k = 9156979, sigma_4(k)/k = 241153415598179286943.
Links
- Giovanni Resta, Table of n, a(n) for n = 1..41 (terms < 5*10^12)
Programs
-
Magma
[n: n in [1..10000000]|IsIntegral(DivisorSigma(2,n)/n) and IsIntegral(DivisorSigma(4,n)/n)]; // Marius A. Burtea, Aug 28 2019
-
Mathematica
Select[Range[10^7], And @@ Divisible[DivisorSigma[{2, 4}, #], #] &] (* Amiram Eldar, Jan 20 2020 *) -
PARI
isok(n) = !(sigma(n, 2) % n) && !(sigma(n, 4) % n); \\ Michel Marcus, Aug 28 2019
Extensions
More terms from T. D. Noe, Apr 11 2006
a(11)-a(12) from Michel Marcus, Aug 28 2019
a(13)-a(18) from Amiram Eldar, Jan 20 2020
a(19)-a(24) from Giovanni Resta, Jan 21 2020