A152215 Numbers k such that sigma_2(k)/(sigma_1(k)*sigma_0(k)) = c, c an integer.

1, 4, 25, 100, 121, 256, 289, 484, 529, 841, 1156, 1600, 1681, 2116, 2209, 2809, 3025, 3364, 3481, 5041, 6400, 6724, 6889, 7225, 7921, 8836, 10201, 11236, 11449, 12100, 12769, 13225, 13924, 17161, 18225, 18496, 18769, 20164, 21025, 22201, 27556, 27889, 28900

Offset: 1

Author

Ctibor O. Zizka, Nov 29 2008

Keywords

• easy
• nonn

Comments

k : A001157(k)/(A000203(k)*A000005(k)) = c, c an integer.

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000005, A000203, A001157, A003601, A094471, A140480, A003601, A020486, A020487

Programs

Mathematica

Select[Range[50000],IntegerQ[DivisorSigma[2,#]/(DivisorSigma[1,#] DivisorSigma[ 0,#])]&] (* Harvey P. Dale, Feb 12 2013 *)

PARI

isok(k) = denominator(sigma(k,2)/(sigma(k, 1)*sigma(k,0))) == 1; \\ Michel Marcus, Jul 15 2019

Extensions

More terms from Harvey P. Dale, Feb 12 2013