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A221856 Square numbers n for which sigma(n) + d(n) is also a perfect square. 1

%I #16 Apr 10 2013 17:32:05

%S 9,16,36,278784,251381025,2390623236,240055902025,354328515025,

%T 1022960302225,1298266542225,6824670333649,9433221536025,

%U 16614933604164,33314541015625,474897452948164,500279020818724,1387202986290276,2162188899431649,16053088159411524

%N Square numbers n for which sigma(n) + d(n) is also a perfect square.

%e 16 is in the list since 16 = 4^2 and sigma(16)+d(16) = 36 = 6^2. Also 278784 = 528^2 and sigma(278784)+d(278784) = 883600 = 940^2.

%t Sqd[n_] := Sqrt[DivisorSigma[1, n] + DivisorSigma[0, n]]; t = {}; Do[If[IntegerQ[Sqd[n^2]], AppendTo[t, n^2]], {n, 1500000}];t

%Y Cf. A007503.

%K nonn

%O 1,1

%A _Jayanta Basu_, Apr 10 2013

%E a(11)-a(19) from _Donovan Johnson_, Apr 10 2013

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Last modified March 28 05:02 EDT 2024. Contains 371235 sequences. (Running on oeis4.)