OFFSET
0,2
LINKS
Masao Koike, Modular forms on non-compact arithmetic triangle groups, Unpublished manuscript [Extensively annotated with OEIS A-numbers by N. J. A. Sloane, Feb 14 2021. I wrote 2005 on the first page but the internal evidence suggests 1997.] See page 29.
MAPLE
A341305 := proc(n)
local a;
a := A013973(n);
if modp(n, 3) = 0 then
a := a+27*A013973(n/3) ;
end if;
%/28 ;
end proc:
seq(A341305(n), n=0..10) ; # R. J. Mathar, Feb 22 2021
MATHEMATICA
A013973[n_] := If[n == 0, 1, -504 DivisorSigma[5, n]];
CROSSREFS
KEYWORD
sign
AUTHOR
N. J. A. Sloane, Feb 13 2021
STATUS
approved