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A337988 Numbers that are the sum of the squares of two of their distinct divisors.

%I A337988 #25 Feb 01 2021 19:21:54
%S A337988 20,80,90,180,272,320,360,468,500,650,720,810,980,1088,1280,1332,1440,
%T A337988 1620,1872,2000,2250,2420,2448,2450,2600,2880,2900,3240,3380,3600,
%U A337988 3920,4160,4212,4352,4410,4500,5120,5328,5760,5780,5850,6480,6642,6800,7220,7290,7488,7650
%N A337988 Numbers that are the sum of the squares of two of their distinct divisors.
%H A337988 Chai Wah Wu, <a href="/A337988/b337988.txt">Table of n, a(n) for n = 1..10000</a>
%H A337988 <a href="/index/Su#ssq">Index entries for sequences related to sums of squares</a>
%e A337988 20 = 2^2 + 4^2, so 20 is in the sequence.
%t A337988 Select[Range[10^4], 1 == Catch@ Do[Do[If[#2[[i]]^2 + #2[[j]]^2 == #1, Throw[1]], {j, i + 1, #3}], {i, #3}] & @@ {#, Divisors[#], DivisorSigma[0, #]} &] (* _Michael De Vlieger_, Oct 10 2020 *)
%o A337988 (PARI) isok(m) = {my(d=divisors(m)); for (i=2, #d, for (j=1, i-1, if (d[i]^2+d[j]^2 == m, return (1));););} \\ _Michel Marcus_, Oct 07 2020
%o A337988 (Python)
%o A337988 from sympy import divisors, integer_nthroot
%o A337988 A337988_list = []
%o A337988 for n in range(1,10**6):
%o A337988     for d in divisors(n):
%o A337988         if 2*d*d >= n:
%o A337988             break
%o A337988         a, b = integer_nthroot(n-d*d,2)
%o A337988         if b and n % a == 0:
%o A337988             A337988_list.append(n)
%o A337988             break # _Chai Wah Wu_, Oct 30 2020
%Y A337988 Cf. A000404.
%K A337988 nonn
%O A337988 1,1
%A A337988 _Wesley Ivan Hurt_, Oct 06 2020
%E A337988 More terms from _Michel Marcus_, Oct 07 2020