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A025313 Numbers that are the sum of 2 distinct nonzero squares in 3 or more ways. 5

%I

%S 325,425,650,725,845,850,925,1025,1105,1300,1325,1445,1450,1525,1625,

%T 1690,1700,1825,1850,1885,2050,2125,2210,2225,2405,2425,2465,2525,

%U 2600,2650,2665,2725,2825,2873,2890,2900,2925,3050,3125,3145,3250,3380,3400

%N Numbers that are the sum of 2 distinct nonzero squares in 3 or more ways.

%C Sequence contains no primes (A000040) and no semiprimes (A001358). - Zak Seidov, Apr 07 2011

%C Sequences A025294 and A025313 are different. For example 1250 is not in A025313. A025294(9) = 1250 = 35^2 + 5^2 = 31^2 + 17^2 = 25^2 + 25^2 (not distinct squares). - _Vaclav Kotesovec_, Feb 27 2016

%C Numbers in A025294 but not in A025313 are exactly those numbers of the form 2*p_1^(2*a_1)*p_2^(2*a_2)*...*p_m^(2*a_m)*q^4 where p_i are primes of the form 4k+3 and q is a prime of the form 4k+1. Thus 2*5^4 = 1250 is the smallest term in A025294 that is not in A025313. - _Chai Wah Wu_, Feb 27 2016

%H Zak Seidov, <a href="/A025313/b025313.txt">Table of n, a(n) for n = 1..5386</a>

%H <a href="/index/Su#ssq">Index entries for sequences related to sums of squares</a>

%e 325 = 1^2+18^2 = 6^2+17^2 = 10^2+15^2. [Zak Seidov, Apr 07 2011]

%t nn = 3400; t = Table[0, {nn}]; lim = Floor[Sqrt[nn - 1]]; Do[num = i^2 + j^2; If[num <= nn, t[[num]]++], {i, lim}, {j, i - 1}]; Flatten[Position[t, _?(# >= 3 &)]] (* _T. D. Noe_, Apr 07 2011 *)

%K nonn

%O 1,1

%A _David W. Wilson_

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Last modified January 18 19:19 EST 2020. Contains 331029 sequences. (Running on oeis4.)