OFFSET
1,3
LINKS
FORMULA
a(n) is multiplicative with a(2^e) = 1, a(17^e) = (-1)^e. For p prime, a(p^e) = a(p) * a(p^(e-1)) - p * a(p^(e-2)) and a(p) = p minus number of points of elliptic curve modulo p.
a(2*n) = a(n).
G.f. is a period 1 Fourier series which satisfies f(-1 / (34 t)) = 34 (t/i)^2 f(t) where q = exp(2 Pi i t).
EXAMPLE
G.f. = q + q^2 - 2*q^3 + q^4 - 2*q^6 - 4*q^7 + q^8 + q^9 + 6*q^11 - 2*q^12 + ...
PROG
(PARI) {a(n) = if( n<1, 0, ellak( ellinit([ 1, 0, 0, -3, 1], 1), n))};
(Magma) A := Basis( CuspForms( Gamma0(34), 2), 77); A[1] + A[2] - 2*A[3];
(Sage) A = CuspForms( Gamma0(34), 2, prec = 77) . basis(); A[0] + A[1] - 2*A[2];
CROSSREFS
KEYWORD
sign,mult
AUTHOR
Michael Somos, Apr 07 2015
STATUS
approved