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 A071010 #14 May 13 2022 04:54:59 %S A071010 1,3,2,3,7,6,6,5,8,9,6,15,10,14,18,8,12,12,15,14,24,11,21,18,12,31,18, %T A071010 30,18,30,20,15,42,24,26,36,17,24,36,18,31,35,24,42,20,21,56,33,30,45, %U A071010 28,42,32,36,30,63,39,54,26,48,27,70,54,38,62,60,36,45,36,90,42,56,78 %N A071010 Sigma(k)/4 when k is not a sum of 2 squares. %C A071010 Conjecture : if n is not the sum of 2 squares sigma(n) == 0 (mod 4) (converse is not true : if sigma(n) == 0 (mod 4), n is sometimes the sum of 2 squares : sigma(65) = 84 == 0 (mod 4) but 65 = 49+16 is a sum of 2 squares). %H A071010 Amiram Eldar, <a href="/A071010/b071010.txt">Table of n, a(n) for n = 1..10000</a> %F A071010 a(n) = sigma(A022544(n))/4. %t A071010 DivisorSigma[1, Select[Range[120], SquaresR[2, #] == 0 &]]/4 (* _Amiram Eldar_, May 13 2022 *) %o A071010 (PARI) for(n=0,200,if(sum(i=0,n,sum(j=0,i,if(i^2+j^2-n,0,1)))==0,print1(sigma(n)/4,","))) %Y A071010 Cf. A000203, A022544. %K A071010 easy,nonn %O A071010 1,2 %A A071010 _Benoit Cloitre_, May 19 2002