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 A081866 #14 Jan 08 2025 02:46:32
%S A081866 1,19684,1953126,40353608,387440173,2357947692,10604499374,
%T A081866 38445332184,118587876498,322687697780,794320419872,1801152661464,
%U A081866 3814699218751,7625984925160,14507145975870,26439622160672,46413842369328,78815680978608,129961739795078,208738965677816
%N A081866 a(n) = sigma_9(2n-1).
%H A081866 Harvey P. Dale, <a href="/A081866/b081866.txt">Table of n, a(n) for n = 1..1000</a>
%F A081866 Sum_{k=1..n} a(k) ~ c * n^10, where c = 31 * Pi^10 / 56700 = 51.200872... . - _Amiram Eldar_, Jan 08 2025
%t A081866 DivisorSigma[9,Range[1,41,2]] (* _Harvey P. Dale_, Dec 01 2013 *)
%o A081866 (PARI) a(n) = sigma(2*n-1, 9); \\ _Amiram Eldar_, Jan 08 2025
%Y A081866 Cf. A013957.
%K A081866 nonn
%O A081866 1,2
%A A081866 _Benoit Cloitre_, Apr 12 2003