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A121362 Expansion of eta(q)*eta(q^6)*eta(q^10)*eta(q^15)/(eta(q^3)*eta(q^5)) in powers of q. 4
1, -1, -1, 1, -1, 1, 0, -1, 1, 1, 0, -1, 0, 0, 1, 1, -2, -1, 2, -1, 0, 0, -2, 1, 1, 0, -1, 0, 0, -1, 2, -1, 0, 2, 0, 1, 0, -2, 0, 1, 0, 0, 0, 0, -1, 2, -2, -1, 1, -1, 2, 0, -2, 1, 0, 0, -2, 0, 0, 1, 2, -2, 0, 1, 0, 0, 0, -2, 2, 0, 0, -1, 0, 0, -1, 2, 0, 0, 2, -1, 1, 0, -2, 0, 2, 0, 0, 0, 0, 1, 0, -2, -2, 2, -2, 1, 0, -1, 0, 1, 0, -2, 0, 0, 0 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,17

COMMENTS

Ramanujan theta functions: f(q) := Product_{k>=1} (1-(-q)^k) (see A121373), phi(q) := theta_3(q) := Sum_{k=-oo..oo} q^(k^2) (A000122), psi(q) := Sum_{k=0..oo} q^(k*(k+1)/2) (A010054), chi(q) := Product_{k>=0} (1+q^(2k+1)) (A000700).

LINKS

G. C. Greubel, Table of n, a(n) for n = 1..1000

M. Somos, Introduction to Ramanujan theta functions

Eric Weisstein's World of Mathematics, Ramanujan Theta Functions

FORMULA

Euler transform of period 30 sequence [ -1, -1, 0, -1, 0, -1, -1, -1, 0, -1, -1, -1, -1, -1, 0, -1, -1, -1, -1, -1, 0, -1, -1, -1, 0, -1, 0, -1, -1, -2, ...].

Expansion of q*f(-q)f(-q^15)/(chi(-q^3)chi(-q^5)) in powers of q where f(),chi() are Ramanujan theta functions.

G.f.: x Product_{n>0} (1-x^n)(1+x^(3n))(1+x^(5n))(1-x^(15n)).

a(n) is multiplicative with a(2^e)=a(3^e)=a(5^e)=(-1)^e, a(p^e) = e+1 if p == 1,4 (mod 15), a(p^e) = (-1)^e*(e+1) if p == 2,8 (mod 15), a(p^e) = (1+( -1)^e)/2 if p == 7,11,13,14 (mod 15).

MATHEMATICA

eta[q_] := q^(1/24)*QPochhammer[q]; a[n_]:= SeriesCoefficient[eta[q]* eta[q^6]*eta[q^10]*eta[q^15]/(eta[q^3]*eta[q^5]), {q, 0, n}]; Table[a[n], {n, 1, 50}] (* G. C. Greubel, Feb 11 2018 *)

PROG

(PARI) {a(n)=local(A); if(n<1, 0, n--; A=x*O(x^n); polcoeff( eta(x+A)*eta(x^6+A)*eta(x^10+A)*eta(x^15+A)/(eta(x^3+A)*eta(x^5+A)), n))}

CROSSREFS

Cf. A082451(n) = |a(n)|.

Sequence in context: A048622 A105661 A082451 * A234694 A091704 A175799

Adjacent sequences:  A121359 A121360 A121361 * A121363 A121364 A121365

KEYWORD

sign,mult

AUTHOR

Michael Somos, Jul 22 2006

STATUS

approved

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Last modified June 25 21:43 EDT 2019. Contains 324357 sequences. (Running on oeis4.)