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Sqrt(sigma(A008847(n)^2)), where A008847 lists m such that sigma(m^2) is a square.
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%I #17 May 06 2016 12:59:53

%S 1,11,31,341,1729,2821,19019,31031,43617,43491,68961,72219,82677,

%T 86583,117831,117831,187131,347529,347529,479787,503347,414309,436107,

%U 496713,478401,503347,758571,794409,909447,952413,658749,696787,696787

%N Sqrt(sigma(A008847(n)^2)), where A008847 lists m such that sigma(m^2) is a square.

%C Note that a(k)=a(k+1) for k=15, 18, 32, 90, 231,... - _Zak Seidov_, May 02 2016

%H Zak Seidov and Donovan Johnson, <a href="/A163763/b163763.txt">Table of n, a(n) for n = 1..400</a> (first 161 terms from Zak Seidov)

%t Select[Sqrt@ DivisorSigma[1, #^2] &@ Range[10^6], IntegerQ] (* _Michael De Vlieger_, May 02 2016, after _Harvey P. Dale_ at A008847 *)

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

%Y Cf. A163764.

%K nonn

%O 1,2

%A _M. F. Hasler_, Aug 03 2009