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 A373881 #35 Mar 30 2025 04:23:56
%S A373881 7,147,4169,132451,4187857,132459677,4188781437,132461190717,
%T A373881 4188790061109,132461176423805,4188790203273025,132461176878317635
%N A373881 Number of lattice points inside the ball x^2 + y^2 + z^2 <= 10^n.
%F A373881 a(n) = A117609(10^n).
%F A373881 Limit_{n->oo} a(n) = (4*Pi/3)*(10^n)^(3/2). - _Hugo Pfoertner_, Jun 21 2024
%o A373881 (PARI) b(k, n) = my(q='q+O('q^(n+1))); polcoef((eta(q^2)^5/(eta(q)^2*eta(q^4)^2))^k/(1-q), n);
%o A373881 a(n) = b(3, 10^n);
%Y A373881 Cf. A068785, A373882, A373883, A373884, A373885, A373896.
%Y A373881 Cf. A000605, A117609.
%K A373881 nonn,more
%O A373881 0,1
%A A373881 _Seiichi Manyama_, Jun 21 2024
%E A373881 a(7)-a(10) from _Hugo Pfoertner_, Jun 21 2024
%E A373881 a(11) from _Chai Wah Wu_, Jun 24 2024