A163764 a(n) = sqrt(sigma(2*m^2)), where m = A097023(n), i.e., sigma(2m^2) is a square.

543, 651, 5187, 5973, 7161, 8463, 57057, 93093, 66063, 81003, 80199, 98553, 130851, 160797, 216657, 259749, 347529, 561393, 565383, 726693, 882189, 1042587, 1084083, 922467, 1439361, 1242927, 1768767, 1490139, 2383227, 2857239, 2029143, 2486169, 4517877, 6175323

Offset

1,1

Links

Amiram Eldar, Table of n, a(n) for n = 1..200 (calculated using the b-file at A097023)

Mathematica

Select[Table[Sqrt[DivisorSigma[1, 2 n^2]], {n, 1000000}], IntegerQ[#] &] (* Tanya Khovanova, Jun 18 2021)

Crossrefs

Cf. A000203, A008847, A097023, A163763.

Sequence in context: A325217 A232707 A334771 * A268146 A074888 A250854

Adjacent sequences: A163761 A163762 A163763 * A163765 A163766 A163767

Keyword

nonn

Author

M. F. Hasler, Aug 03 2009

Extensions

a(31)-a(34) from Amiram Eldar, Aug 13 2024

Status

approved