A243810 Odd squares which are the sum of the divisors of some n.

1, 121, 961, 116281, 294849, 423801, 2989441, 7958041, 26904969, 35676729, 51279921, 71622369, 361722361, 962922961, 1891467081, 1902442689, 3255501249, 4364319969, 4755619521, 5215583961, 6431879601, 6561486009, 6835486329, 7496615889, 8666306649, 9712693809

Offset: 1

Author

Michel Marcus, Jun 11 2014

Keywords

• nonn

Comments

Odd terms of A038688, where most of the terms are even.

The corresponding values in A228061 are: 1, 11, 31, 341, 543, 651, 1729, 2821, ...

Among the known terms, the only prime powers are 121 and 961.

Next term is greater than 10^8.

Examples

			121 being an odd square and satisfying sigma(81) = 121, 121 is in the sequence.
		

Links

• Hiroaki Yamanouchi, Table of n, a(n) for n = 1..183

Crossrefs

Cf. A000203, A038688, A228061.

Programs

Mathematica

Select[DivisorSigma[1,Range[72000000]],OddQ[#]&&IntegerQ[Sqrt[#]]&] (* Harvey P. Dale, Aug 18 2014 *)

Extensions

a(13)-a(26) from Hiroaki Yamanouchi, Sep 27 2014