A163763 Sqrt(sigma(A008847(n)^2)), where A008847 lists 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

Offset: 1

Author

M. F. Hasler, Aug 03 2009

Keywords

• nonn

Comments

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

Links

• Zak Seidov and Donovan Johnson, Table of n, a(n) for n = 1..400 (first 161 terms from Zak Seidov)

Crossrefs

Cf. A163764.

Programs

Mathematica

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

PARI

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