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.
%I A124983 #11 Mar 12 2020 07:23:10
%S A124983 1,9,45,49,81,117,121,153,245,261,333,361,369,405,441,477,529,549,605,
%T A124983 637,657,729,801,833,873,909,961,981,1017,1053,1089,1233,1341,1377,
%U A124983 1413,1421,1557,1573,1629,1737,1773,1805,1813,1849,2009,2057,2061,2097,2169
%N A124983 Nonprime numbers == 1 (mod 4) with a unique partition as a sum of 2 squares x^2 + y^2.
%C A124983 Intersection of A124982 and A125018. - _Michel Marcus_, Nov 02 2013
%H A124983 Amiram Eldar, <a href="/A124983/b124983.txt">Table of n, a(n) for n = 1..10000</a>
%t A124983 Select[4 * Range[0, 500] + 1, !PrimeQ[#] && Length @ PowersRepresentations[#, 2, 2] == 1 &] (* _Amiram Eldar_, Mar 12 2020 *)
%o A124983 (PARI) isok(n)= {if (isprime(n) || (n % 4 != 1), return (0)); A000161(n) == 1;} \\ _Michel Marcus_, Nov 02 2013
%Y A124983 Cf. A000161, A002145, A124982, A125018, A125020.
%K A124983 nonn
%O A124983 1,2
%A A124983 _Artur Jasinski_, Nov 16 2006
%E A124983 More terms from _Michel Marcus_, Nov 02 2013