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A074388 Solutions to sigma[2*(x^2)]=odd^2. 0
195938, 224450, 13645088, 15870978, 18180450, 29184800, 1105252128, 2363968800, 2686005218, 2917410498, 3564550178, 5056357922, 8442721568, 10814792450, 18587462432, 21292224800, 48666384162, 140836104992 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..18.

EXAMPLE

m=195938=2.313.313 and sigma[195938]=294849=543.543 and 543=3.181 odd nonprime. No odd prime solutions were found below 10^12.

MATHEMATICA

Do[s=DivisorSigma[1, 2*(n^2)]; If[IntegerQ[Sqrt[s]]&&Mod[s, 2]==1, Print[2*(n^2)]], {n, 1, 10000000}]

CROSSREFS

Cf. A000203, A001248, A028982, A074386.

Sequence in context: A129486 A203047 A309190 * A234996 A234389 A234393

Adjacent sequences:  A074385 A074386 A074387 * A074389 A074390 A074391

KEYWORD

nonn

AUTHOR

Labos Elemer, Aug 22 2002

STATUS

approved

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Last modified September 21 07:28 EDT 2021. Contains 347596 sequences. (Running on oeis4.)