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 A063200 #24 Jan 29 2024 04:10:25
%S A063200 1,2,4,4,6,8,8,10,12,12,14,16,16,18,20,20,22,24,24,26,28,28,30,32,32,
%T A063200 34,36,36,38,40,40,42,44,44,46,48,48,50,52,52,54,56,56,58,60,60,62,64,
%U A063200 64,66
%N A063200 Dimension of the space of weight 2n cuspidal newforms for Gamma_0( 15 ).
%H A063200 Paolo Xausa, <a href="/A063200/b063200.txt">Table of n, a(n) for n = 1..10000</a>
%H A063200 G. Martin, <a href="http://dx.doi.org/10.1016/j.jnt.2004.10.009">Dimensions of the spaces of cusp forms and newforms on Gamma_0(N) and Gamma_1(N)</a>, J. Numb. Theory 112 (2005) 298-331, Theorem 1.
%H A063200 William A. Stein, <a href="http://wstein.org/Tables/dimskg0new.gp">Dimensions of the spaces S_k^{new}(Gamma_0(N))</a>.
%H A063200 William A. Stein, <a href="http://wstein.org/Tables/">The modular forms database</a>.
%H A063200 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (1,0,1,-1).
%F A063200 G.f.: x +2*x^2*(1+x) / ( (1+x+x^2)*(x-1)^2 ). - _R. J. Mathar_, Jul 15 2015
%F A063200 Sum_{n>=1} (-1)^(n+1)/a(n) = 1- Pi/8. - _Amiram Eldar_, Jan 12 2024
%t A063200 LinearRecurrence[{1, 0, 1, -1}, {1, 2, 4, 4, 6}, 100] (* _Paolo Xausa_, Jan 29 2024 *)
%o A063200 (Python)
%o A063200 def A063200(n): return n-1+sum(divmod(n-1,3)) if n > 1 else 1 # _Chai Wah Wu_, Jan 29 2023
%K A063200 nonn
%O A063200 1,2
%A A063200 _N. J. A. Sloane_, Jul 10 2001