OFFSET
1,1
LINKS
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 (1,1,-1).
FORMULA
Except for the first term, a(n) = 26*(n-1) - a(n-1) (with a(2)=19). - Vincenzo Librandi, Dec 07 2010
From M. F. Hasler, Mar 05 2012: (Start)
a(n+2) = a(n) + 26 (n > 1);
a(2n+1) = a(2n) + 14 (n > 0);
a(2n) = a(2n-1) + 12 (n > 1);
a(n) = 13n - { 6 if n = 2k+1, k > 0; 7 otherwise }.
G.f.: x*(6 + 13*x + 8*x^2 - x^3)/(1 - x - x^2 + x^3). (End)
Sum_{n>=1} (-1)^(n+1)/a(n) = 1/42 + tan(3*Pi/13)*Pi/26 . - Amiram Eldar, Jan 12 2024
MATHEMATICA
Join[{6}, Table[13*n - (13 + (-1)^n)/2, {n, 2, 50}]] (* Amiram Eldar, Jan 12 2024 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Jul 10 2001
STATUS
approved