OFFSET
1,2
LINKS
Paolo Xausa, Table of n, a(n) for n = 1..10000
G. Martin, Dimensions of the spaces of cusp forms and newforms on Gamma_0(N) and Gamma_1(N), J. Numb. Theory 112 (2005) 298-331, Theorem 1.
William A. Stein, Dimensions of the spaces S_k^{new}(Gamma_0(N)).
William A. Stein, The modular forms database.
Index entries for linear recurrences with constant coefficients, signature (1,0,1,-1).
FORMULA
G.f.: x +2*x^2*(1+x) / ( (1+x+x^2)*(x-1)^2 ). - R. J. Mathar, Jul 15 2015
Sum_{n>=1} (-1)^(n+1)/a(n) = 1- Pi/8. - Amiram Eldar, Jan 12 2024
MATHEMATICA
LinearRecurrence[{1, 0, 1, -1}, {1, 2, 4, 4, 6}, 100] (* Paolo Xausa, Jan 29 2024 *)
PROG
(Python)
def A063200(n): return n-1+sum(divmod(n-1, 3)) if n > 1 else 1 # Chai Wah Wu, Jan 29 2023
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Jul 10 2001
STATUS
approved