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

1,2

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.

Links

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

Example

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

Mathematica

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

Crossrefs

Cf. A000203, A038688, A228061.

Sequence in context: A362319 A211472 A223389 * A302561 A120353 A175983

Adjacent sequences: A243807 A243808 A243809 * A243811 A243812 A243813

Keyword

nonn

Author

Michel Marcus, Jun 11 2014

Extensions

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

Status

approved