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 A214295 a(n) = 1 if n is a square, -1 if n is three times a square, 0 otherwise. 4
 1, 0, -1, 1, 0, 0, 0, 0, 1, 0, 0, -1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, -1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Ramanujan theta functions: f(q) (see A121373), phi(q) (A000122), psi(q) (A010054), chi(q) (A000700). a(A092206(n)) = 0; a(A000290(n)) = 1; a(A033428(n)) = -1. LINKS Reinhard Zumkeller, Table of n, a(n) for n = 1..10000 S. Cooper and M. Hirschhorn, On some infinite product identities, Rocky Mountain J. Math., 31 (2001) 131-139. see p. 133 Theorem 3. Eric Weisstein's World of Mathematics, Ramanujan Theta Functions FORMULA Expansion of q * psi(q^3) * f(-q^2, -q^10) / f(-q^5, -q^7) in powers of q where psi(), f() are Ramanujan theta functions. Multiplicative with a(3^e) = (-1)^e, a(p^e) = 1 if e even, 0 otherwise. G.f.: (theta_3(q) - theta_3(q^3)) / 2 = Sum_{k>0} x^(k^2) - x^(3*k^2). Dirichlet g.f.: zeta(2*s) * (1 - 3^-(2*s)). a(3*n) = - a(n). - Reinhard Zumkeller, Jul 12 2012 Expansion of (phi(q) - phi(q^3)) / 2 = q * chi(q) * f(-q, -q^11) in powers fof q where phi(), chi(), f() are Ramanujan theta functions. - Michael Somos, Jan 10 2015 Euler transform of period 12 sequence [ 0, -1, 1, 0, 1, -1, 1, 0, 1, -1, 0, -1, ...]. - Michael Somos, Jan 10 2015 Convolution product of A000700 and A247133. - Michael Somos, Jan 10 2015 EXAMPLE G.f. = q - q^3 + q^4 + q^9 - q^12 + q^16 + q^25 - q^27 + q^36 - q^48 + q^49 + ... MATHEMATICA a[ n_] := SeriesCoefficient[ (EllipticTheta[ 3, 0, q] - EllipticTheta[ 3, 0, q^3]) / 2, {q, 0, n}]; a[ n_] := Boole[ IntegerQ[ Sqrt[ n]]] - Boole[ IntegerQ[ Sqrt[ 3 n]]]; (* Michael Somos, Jun 10 2014 *) Table[Which[IntegerQ[Sqrt[n]], 1, IntegerQ[Sqrt[n/3]], -1, True, 0], {n, 120}] (* Harvey P. Dale, Apr 08 2013 *) PROG (PARI) {a(n) = issquare(n) - issquare(3*n)}; (PARI) {a(n) = if( n<1, 0, direuler( p=2, n, if( p==3, 1 - X, 1) / (1 - X^2 ))[n])}; (Haskell) a214295 n = a010052 n - a010052 (3*n)  -- Reinhard Zumkeller, Jul 12 2012 (MAGMA) Basis( ModularForms( Gamma1(12), 1/2), 50) [2] ; /* Michael Somos, Jun 10 2014 */ CROSSREFS Cf. A000700, A010052, A247133. Sequence in context: A266377 A266326 A185295 * A145377 A246260 A275973 Adjacent sequences:  A214292 A214293 A214294 * A214296 A214297 A214298 KEYWORD sign,mult AUTHOR Michael Somos, Jul 10 2012 STATUS approved

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Last modified January 16 19:43 EST 2019. Contains 319206 sequences. (Running on oeis4.)