A145450 Numbers k such that k/A000005(k) is a square.

1, 2, 36, 108, 128, 225, 288, 441, 450, 600, 864, 882, 1089, 1176, 1521, 1944, 2000, 2178, 2601, 2904, 3042, 3240, 3249, 4056, 4761, 5202, 6144, 6498, 6561, 6936, 7569, 8649, 8664, 9522, 10000, 11760, 12321, 12696, 13122, 15129, 15138, 16641, 17298

Offset: 1

Author

Ctibor O. Zizka, Oct 10 2008

Keywords

• nonn

Comments

Subsequence of A033950.

Examples

			36/A000005(36) = 36/9 = 4 = 2^2, hence 36 is in the sequence.
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..5479 (terms below 10^9)

Crossrefs

Cf. A000005 (sigma_0, number of divisors of n), A033950 (refactorable numbers), A140480 (RMS numbers).

Programs

Mathematica

Select[Range[20000],IntegerQ[Sqrt[#/DivisorSigma[0,#]]]&] (* Harvey P. Dale, May 21 2012 *)

PARI

{m=18000; for(n=1, m, s=sigma(n,0); if(n%s==0&&issquare(n/s), print1(n,",")))}

Extensions

Edited and extended by Klaus Brockhaus, Oct 15 2008