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 A000508 M5324 N2315 #47 Oct 25 2024 10:05:56
%S A000508 61,2763,38528,249856,1066590,3487246,9493504,22634496,48649086,
%T A000508 96448478,179369856,315621376,530788622,860061996,1346126848,
%U A000508 2046820352,3038120316,4403100222,6254596992,8737505280,11992903772
%N A000508 Generalized class numbers c_(n,3).
%C A000508 Let L_a(s) = Sum_{k>=0} (-a|2k+1) /(2k+1)^s be a Dirichlet series, where (-a|2k+1) is the Jacobi symbol. Then the c_(a,n) are defined by L_a(2n+1) = (Pi/(2a))^(2n+1)*sqrt(a)*c_(a,n)/(2n)! for n=0,1,2,..., a=1,2,3,...
%D A000508 N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
%D A000508 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H A000508 Matthew House, <a href="/A000508/b000508.txt">Table of n, a(n) for n = 1..10000</a>
%H A000508 D. Shanks, <a href="http://dx.doi.org/10.1090/S0025-5718-1967-0223295-5">Generalized Euler and class numbers</a>, Math. Comp. 21 1967 6890694.
%H A000508 D. Shanks, <a href="http://dx.doi.org/10.1090/S0025-5718-1968-0227093-9">Corrigenda to: "Generalized Euler and class numbers"</a>, Math. Comp. 22 (1968), 699
%H A000508 D. Shanks, <a href="/A000003/a000003.pdf">Generalized Euler and class numbers</a>, Math. Comp. 21 (1967), 689-694; 22 (1968), 699. [Annotated scanned copy]
%t A000508 amax = 25; km0 = 10; Clear[cc]; L[a_, s_, km_] := Sum[ JacobiSymbol[ -a, 2 k + 1]/(2 k + 1)^s, {k, 0, km}]; c[1, n_, km_] := 2 (2 n)! L[1, 2 n + 1, km] (2/Pi)^(2 n + 1) // Round; c[a_ /; a > 1, n_, km_] := (2 n)! L[a, 2 n + 1, km] (2 a/Pi)^(2 n + 1)/Sqrt[a] // Round; cc[km_] := cc[km] = Table[ c[a, 3, km], {a, 1, amax} ]; cc[km0]; cc[km = 2 km0]; While[cc[km] != cc[km/2, km = 2 km]]; A000508 = cc[km] (* _Jean-François Alcover_, Feb 09 2016 *)
%t A000508 Table[rowA235605[n, 3][[4]], {n, 50}] (* see A235605 *) (* _Matthew House_, Oct 05 2024 *)
%Y A000508 Column 3 of A235605.
%Y A000508 Cf. A000003, A000233, A000362.
%K A000508 nonn,easy
%O A000508 1,1
%A A000508 _N. J. A. Sloane_
%E A000508 More terms from Kok Seng Chua (chuaks(AT)ihpc.nus.edu.sg), Jun 02 2000
%E A000508 Name clarified by _James C. McMahon_, Nov 30 2023