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A214960 Expansion of psi(x^2) - x * psi(x^10) in powers of x where psi() is a Ramanujan theta function. 2
1, -1, 1, 0, 0, 0, 1, 0, 0, 0, 0, -1, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, -1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, -1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

COMMENTS

Ramanujan theta functions: f(q) (see A121373), phi(q) (A000122), psi(q) (A010054), chi(q) (A000700).

LINKS

G. C. Greubel, Table of n, a(n) for n = 0..1000

R. Blecksmith; J. Brillhart; I. Gerst, Some infinite product identities, Math. Comp. 51 (1988), no. 183, 301-314. see p. 310.

S. Cooper and M. Hirschhorn, On some infinite product identities, Rocky Mountain J. Math., 31 (2001) 131-139. see p. 134 Theorem 6.

M. Somos, Introduction to Ramanujan theta functions

Eric Weisstein's World of Mathematics, Ramanujan Theta Functions

FORMULA

Expansion of f(-x, -x^4) * f(-x^2, x^3) / f(-x^2, -x^2) = f(-x, x^4) * f(x^2, x^3) / f(-x^10, -x^10) in powers of x where f(,) is Ramanujan's two-variable theta function.

Euler transform of period 20 sequence [ -1, 1, 1, 0, 0, 0, 1, 0, -1, -1, -1, 0, 1, 0, 0, 0, 1, 1, -1, -1, ...].

a(n) = b(4*n + 1) where b(n) is multiplicative and b(2^e) = 0^e, b(5^e) = (-1)^e, else b(p^e) = (1 + (-1)^e) / 2.

G.f.: Sum_{k>0} x^(k*(k - 1)) - x^(5*k*(k - 1) + 1) = Product_{k>0} (1 - x^(10*k)) * (1 - x^(10*k - 1)) * (1 + x^(10*k-2)) * (1 + x^(10*k - 3)) * (1 + x^(10*k - 4)) * (1 + x^(10*k - 6)) * (1 + x^(10*k - 7)) * (1 + x^(10*k - 8)) * (1 - x^(10*k - 9)).

a(9*n + 2) = - a(5*n + 1) = a(n), a(5*n + 3) = a(5*n + 4) = a(6*n + 3) = a(6*n + 4) = a(9*n + 5) = a(9*n + 8) = 0.

a(n) = (-1)^n * A127693(n). a(2*n) = A010054(n). a(3*n) = A089806(n). a(6*n) = A080995(n).

EXAMPLE

1 - x + x^2 + x^6 - x^11 + x^12 + x^20 + x^30 - x^31 + x^42 + x^56 - x^61 + ...

q - q^5 + q^9 + q^25 - q^45 + q^49 + q^81 + q^121 - q^125 + q^169 + q^225 + ...

MATHEMATICA

f[x_, y_] := QPochhammer[-x, x*y]*QPochhammer[-y, x*y]*QPochhammer[x*y, x*y]; A214960[n_] := SeriesCoefficient[f[-x, -x^4]*f[-x^2, x^3]/f[-x^2, -x^2], {x, 0, n}]; Table[A214960[n], {n, 0, 50}] (* G. C. Greubel, Jun 18 2017 *)

PROG

(PARI) {a(n) = issquare(4*n + 1) - issquare(20*n + 5)}

(PARI) {a(n) = local(A, p, e); if( n<0, 0, A = factor(4*n + 1); prod( k=1, matsize(A)[1], if( p=A[k, 1], e=A[k, 2]; if( p==2, 0, if( p==5, (-1)^e, (1 + (-1)^e) / 2)))))}

CROSSREFS

Cf. A010054, A080995, A089806, A127693.

Sequence in context: A016362 A016415 A266659 * A127693 A129405 A127001

Adjacent sequences:  A214957 A214958 A214959 * A214961 A214962 A214963

KEYWORD

sign

AUTHOR

Michael Somos, Jul 30 2012

STATUS

approved

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Last modified March 26 20:47 EDT 2019. Contains 321535 sequences. (Running on oeis4.)