Discussion
Fri May 19
10:41
Andy Huchala: I'm still confident this is the same as A004048, but I can't find a reference actually defining Gamma1(N)+ so I'll withdraw my comment.
Discussion
Mon May 15
22:12
Andy Huchala: Per the reference Gross 1996 p. 276, this theta series is a weight 7 modular form on Gamma1(3)+. In "Normalizer of Gamma1(m)" by Lang, it is established that Normalizer(Gamma1(3))=Gamma0(3)+, and in Zemel's "Normalizers of Congruence Groups in SL2(R)
and Automorphisms of Lattices" it's mentioned that Normalizer(Gamma0(3)) = Gamma0(3). I'm still looking for a reference to show that Gamma1(m)+ does in fact denote the normalizer of Gamma1(m) but I believe that's the intended meaning (Wikipedia mentions this for Gamma0(m)+).
All this to say... once I've found a reference (or if anyone can confirm this notation that Gamma1(N)+ means Normalizer(Gamma1(N)) both the theta series from this sequence and A004048 live in M_7(Gamma0(3)), which is 3-dimensional according to magma, so if they agree up to 3 terms they agree at every term.
AUTHOR
_N. J. A. Sloane (njas(AT)research.att.com)_.
Discussion
Fri Mar 30
16:46
OEIS Server: https://oeis.org/edit/global/110
AUTHOR
N. J. A. Sloane (njas(AT)research.att.com).
NAME
Theta series of 14-dim. dimensional lattice of det 3^7 and minimal norm 2.
EXTENSIONS
Possibly the same as A004048?