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Odd squares which are the sum of the divisors of some n.
2

%I #22 Sep 27 2014 16:11:57

%S 1,121,961,116281,294849,423801,2989441,7958041,26904969,35676729,

%T 51279921,71622369,361722361,962922961,1891467081,1902442689,

%U 3255501249,4364319969,4755619521,5215583961,6431879601,6561486009,6835486329,7496615889,8666306649,9712693809

%N Odd squares which are the sum of the divisors of some n.

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

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

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

%C Next term is greater than 10^8.

%H Hiroaki Yamanouchi, <a href="/A243810/b243810.txt">Table of n, a(n) for n = 1..183</a>

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

%t Select[DivisorSigma[1,Range[72000000]],OddQ[#]&&IntegerQ[Sqrt[#]]&] (* _Harvey P. Dale_, Aug 18 2014 *)

%Y Cf. A000203, A038688, A228061.

%K nonn

%O 1,2

%A _Michel Marcus_, Jun 11 2014

%E a(13)-a(26) from _Hiroaki Yamanouchi_, Sep 27 2014