cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

A025287 Numbers that are the sum of 2 nonzero squares in exactly 4 ways.

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%I A025287 #18 Jul 23 2024 13:14:30
%S A025287 1105,1625,1885,2125,2210,2405,2465,2665,3145,3250,3445,3485,3625,
%T A025287 3770,3965,4225,4250,4420,4505,4625,4745,4810,4930,5125,5185,5330,
%U A025287 5365,5785,5945,6205,6290,6305,6409,6500,6565,6625,6890,6970,7085,7225,7250,7345
%N A025287 Numbers that are the sum of 2 nonzero squares in exactly 4 ways.
%H A025287 Donovan Johnson, <a href="/A025287/b025287.txt">Table of n, a(n) for n = 1..1000</a>
%H A025287 <a href="/index/Su#ssq">Index entries for sequences related to sums of squares</a>
%t A025287 nn = 7345; t = Table[0, {nn}]; lim = Floor[Sqrt[nn - 1]]; Do[num = i^2 + j^2; If[num <= nn, t[[num]]++], {i, lim}, {j, i}]; Flatten[Position[t, 4]] (* _T. D. Noe_, Apr 07 2011 *)
%t A025287 nz4Q[n_]:=Count[IntegerPartitions[n,{2}],_?(FreeQ[#,0]&&AllTrue[Sqrt[#],IntegerQ]&)]==4; Select[Range[7500],nz4Q] (* _Harvey P. Dale_, Jul 23 2024 *)
%K A025287 nonn
%O A025287 1,1
%A A025287 _David W. Wilson_