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1, -1, 0, 0, -2, 0, 2, 0, 0, 0, 0, 3, 0, 0, -3, 0, 0, 0, 0, 0, 0, -4, 0, 0, 0, 4, 0, 0, 0, 0, 0, 0, 0, 0, 5, 0, 0, 0, 0, -5, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -6, 0, 0, 0, 0, 0, 6, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 7, 0, 0, 0, 0, 0, 0, -7, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -8, 0, 0, 0, 0, 0, 0, 0, 8, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 9, 0, 0, 0, 0, 0, 0, 0
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OFFSET
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1,5
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COMMENTS
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Ramanujan theta functions: f(q) := Prod_{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) := Prod_{k>=0} (1+q^(2k+1)) (A000700).
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LINKS
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FORMULA
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G.f.: A(x) = Sum_{n>=1} (-1)^(n-1)*n*[x^(n*(3*n-1)/2) - x^(n*(3*n+1)/2)] = x - x^2 - 2*x^5 + 2*x^7 + 3*x^12 - 3*x^15 - 4*x^22 + 4*x^26 + 5*x^35 - 5*x^40 - 6*x^51 + 6*x^57 +...
Expansion of f(-q)* (g(q)-1)/6 in powers of q where f(-q) = g.f. of A010815, g(q) = g.f. of A004016.
Expansion of (f(-q)/ f(-q^3))*(f(-q)^3 -f(-q^3) +9*q*f(-q^9)^3)/6 in powers of q where f() is a Ramanujan theta function. - Michael Somos, Jun 11 2006
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EXAMPLE
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G.f. satisfies 6*A(x^3) = eta(x)^3 - eta(x^3) + 3*x*eta(x^9)^3, where eta(x) = 1 + Sum_{n>=1} (-1)^n*[x^(n*(3*n-1)/2) + x^(n*(3*n+1)/2)] = 1 - x - x^2 + x^5 + x^7 - x^12 - x^15 + x^22 + x^26 +... and eta(x)^3 = 1 - 3*x + 5*x^3 - 7*x^6 + 9*x^10 +... + (-1)^n*(2*n+1)*x^(n*(n+1)/2) + ... is the Jacobi triple product identity.
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MATHEMATICA
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a:= CoefficientList[Series[Sum[(-1)^(n-1)*n*(x^(n*(3*n - 1)/2) - x^(n*(3*n + 1)/2)), {n, 1, 50}], {x, 0, 50}], x]; Drop[Table[a[[n]], {n, 1, 50}], 1] (* G. C. Greubel, May 09 2018 *)
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PROG
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(PARI) {a(n)=local(X=x+x*O(x^(3*n))); polcoeff((eta(X)^3-eta(X^3)+3*x*eta(X^9)^3)/6, 3*n)}
(PARI) {a(n)= local(A); if(n<1, 0, A=x*O(x^n); polcoeff( eta(x+A)/ eta(x^3+A)* (eta(x+A)^3 -eta(x^3+A) +9*x* eta(x^9+A)^3)/6, n))} /* Michael Somos, Jun 11 2006 */
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CROSSREFS
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KEYWORD
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sign
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AUTHOR
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STATUS
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approved
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