A163763 a(n) = sqrt(sigma(A008847(n)^2)), where A008847 lists numbers m such that sigma(m^2) is a square.

1, 11, 31, 341, 1729, 2821, 19019, 31031, 43617, 43491, 68961, 72219, 82677, 86583, 117831, 117831, 187131, 347529, 347529, 479787, 503347, 414309, 436107, 496713, 478401, 503347, 758571, 794409, 909447, 952413, 658749, 696787, 696787, 1296141, 1348221, 828723

Offset

1,2

Comments

Note that a(k) = a(k+1) for k = 15, 18, 32, 90, 231, ... - Zak Seidov, May 02 2016

Links

Amiram Eldar, Table of n, a(n) for n = 1..1000 (terms 1..161 terms from Zak Seidov, terms 162..400 from Donovan Johnson)

Mathematica

Select[Sqrt@ DivisorSigma[1, #^2] &@ Range[10^6], IntegerQ] (* Michael De Vlieger, May 02 2016, after Harvey P. Dale at A008847 *)

Prog

(PARI) lista(nn) = {for (n=1, nn, if (issquare(s = sigma(n^2)), print1(sqrtint(s), ", ")); ); } \\ Michel Marcus, May 02 2016

Crossrefs

Cf. A000203, A008847, A163764.

Sequence in context: A383624 A093881 A328715 * A201808 A111015 A143765

Adjacent sequences: A163760 A163761 A163762 * A163764 A163765 A163766

Keyword

nonn

Author

M. F. Hasler, Aug 03 2009

Status

approved