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A159633 Dimension of Eisenstein subspace of the space of modular forms of weight k/2, level 4*n and trivial character, where k>=5 is odd. 1
2, 3, 4, 6, 4, 6, 4, 8, 8, 6, 4, 12, 4, 6, 8, 12, 4, 12, 4, 12, 8, 6, 4, 16, 12, 6, 12, 12, 4, 12, 4, 16, 8, 6, 8, 24, 4, 6, 8, 16, 4, 12, 4, 12, 16, 6, 4, 24, 16, 18, 8, 12, 4, 18, 8, 16, 8, 6, 4, 24, 4, 6, 16, 24, 8, 12, 4, 12, 8, 12, 4, 32, 4, 6, 24, 12, 8, 12, 4, 24, 24, 6, 4, 24, 8, 6, 8, 16, 4 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Denote dim{M_k(Gamma_0(N))} by m(k,N) and dim{S_k(Gamma_0(N))} by s(k,N).

We have:

m(3/2,N)-s(3/2,N)+m(1/2,N)-s(1/2,N) =

m(5/2,N)-s(5/2,N) = m(7/2,N)-s(7/2,N) =

m(9/2,N)-s(9/2,N) = m(11/2,N)-s(11/2,N) = ...

m(k/2,N)-s(k/2,N) = ...

where N is any positive multiple of 4 and k>=5 is odd.

a(n) = A159635(n) - A159636(n). - Steven Finch, Apr 22 2009

Conjecture: a(n) = 2*chi(n) - if(mod(n+2,4)=0, chi(n)/2, 0) with chi(n) = Sum(d|n; phi(gcd(d,n/d)); checked up to n=1024. - Wouter Meeussen, Apr 02 2014

REFERENCES

K. Ono, The Web of Modularity: Arithmetic of Coefficients of Modular Forms and q-series. American Mathematical Society, 2004 (p. 16, theorem 1.56).

LINKS

Table of n, a(n) for n=1..89.

H. Cohen and J. Oesterle, Dimensions des espaces de formes modulaires, Modular Functions of One Variable. VI, Proc. 1976 Bonn conf., Lect. Notes in Math. 627, Springer-Verlag, 1977, pp. 69-78.

S. R. Finch, Primitive Cusp Forms, April 27, 2009. [Cached copy, with permission of the author]

Peter Humphries, Answer to: "A conjecture related to the Cohen-Oesterlé dimension formula", MathOverflow, 2014.

MAGMA Calculator.

MATHEMATICA

(* see link, conjecture proved by P. Humphries *)

chi[n_Integer]:=Sum[EulerPhi[GCD[d, n/d]], {d, Divisors[n]}];

2 chi[#] - If[Mod[# + 2, 4] == 0, chi[#]/2, 0] & /@ Range[89]

(* Wouter Meeussen, Apr 06 2014 *)

PROG

(MAGMA) [[4*n, Dimension(HalfIntegralWeightForms(4*n, 5/2))-Dimension(CuspidalSubspace(HalfIntegralWeightForms(4*n, 5/2)))] : n in [1..100]]; [[4*n, Dimension(HalfIntegralWeightForms(4*n, 7/2))-Dimension(CuspidalSubspace(HalfIntegralWeightForms(4*n, 7/2)))] : n in [1..100]]; [[4*n, Dimension(HalfIntegralWeightForms(4*n, 3/2))-Dimension(CuspidalSubspace(HalfIntegralWeightForms(4*n, 3/2)))+Dimension(HalfIntegralWeightForms(4*n, 1/2))-Dimension(CuspidalSubspace(HalfIntegralWeightForms(4*n, 1/2)))] : n in [1..100]];

CROSSREFS

Cf. A159630, A159631, A159632, A159634, A159635, A159636. - Steven Finch, Apr 22 2009

Cf. A001616.

Sequence in context: A074103 A051785 A144825 * A049044 A102284 A273098

Adjacent sequences:  A159630 A159631 A159632 * A159634 A159635 A159636

KEYWORD

nonn

AUTHOR

Steven Finch, Apr 17 2009

STATUS

approved

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Last modified April 18 07:59 EDT 2021. Contains 343084 sequences. (Running on oeis4.)