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 A377879 #15 Nov 24 2024 11:27:39
%S A377879 1,1,5,1,19,-19,41,1,41,-17,109,-115,155,-7,47,1,271,-199,341,-161,
%T A377879 141,37,505,-499,469,71,365,-199,811,-1021,929,1,449,163,683,-1159,
%U A377879 1331,221,663,-737,1639,-1659,1805,-251,299,361,2161,-2035,2001,-467,1211,-265,2755,-1819,1927,-967,1545,631,3421,-5293,3659,737
%N A377879 Deficiency of squares: a(n) = 2n^2 - sigma(n^2).
%C A377879 It is conjectured that 1's occur only when n is two's power (A000079), and that there are no -1's in this sequence. See comments in A033879 and in A337339.
%H A377879 Antti Karttunen, <a href="/A377879/b377879.txt">Table of n, a(n) for n = 1..20000</a>
%H A377879 <a href="/index/Si#SIGMAN">Index entries for sequences related to sigma(n)</a>.
%F A377879 a(n) = A033879(A000290(n)).
%t A377879 Table[2n^2-DivisorSigma[1, n^2], {n, 62}] (* _James C. McMahon_, Nov 24 2024 *)
%o A377879 (PARI)
%o A377879 A033879(n) = (n+n-sigma(n));
%o A377879 A377879(n) = A033879(n*n);
%Y A377879 Cf. A000290, A000079 (conjectured to give positions of all 1's), A033879, A378231 [= a(A003961(n))].
%Y A377879 Cf. A000012, A083884.
%Y A377879 Cf. also square array A083064.
%K A377879 sign
%O A377879 1,3
%A A377879 _Antti Karttunen_, Nov 23 2024