A104501 Coefficients of the A-Dyson Mod 27 identity.

1, 1, 2, 3, 5, 7, 11, 15, 22, 30, 42, 56, 76, 100, 133, 172, 225, 288, 371, 470, 598, 751, 945, 1177, 1468, 1815, 2245, 2757, 3386, 4133, 5043, 6121, 7425, 8966, 10818, 13001, 15610, 18677, 22324, 26600, 31662, 37582, 44560, 52701, 62261, 73387, 86406

Offset: 0

Author

Eric W. Weisstein, Mar 11 2005

Keywords

• nonn

Examples

			1 +q +2*q^2 +3*q^3 +5*q^4 +7*q^5 +11*q^6 +15*q^7 +22*q^8 +30*q^9 +...
		

Links

• G. C. Greubel, Table of n, a(n) for n = 0..1000
• Eric Weisstein's World of Mathematics, Dyson Mod 27 Identities

Crossrefs

Cf. A104502, A104503, A104504.

Programs

Mathematica

QP = QPochhammer; (QP[1/x^15, x^27]*QP[1/x^12, x^27]*QP[x^27])/((1-1/x^15)* (1-1/x^12)*QP[x]) + O[x]^50 // CoefficientList[#, x]& (* Jean-François Alcover, Nov 18 2017 *)

PARI

{a(n)=local(m); if(n<0, 0, m=sqrtint(24*n+1); polcoeff( sum(k= -((m-1)\18), (m+1)\18, (-1)^k*x^((9*k^2-k)*3/2),x*O(x^n))/ eta(x+x*O(x^n)), n))} /* Michael Somos, Mar 15 2006 */

PARI

{a(n)=if(n<0, 0, polcoeff( sum(k=1, sqrtint(n), x^k^2* prod(j=1, k-1, (1-x^(3*j))/(1-x^(j+1))/(1-x^(2*j))/(1-x^(2*j+1)), 1+O(x^(n-k^2+1)))/(1-x)^2, 1), n))} /* Michael Somos, Mar 15 2006 */

PARI

{a(n) = local(A); if( n<0, 0, A = eta(x + x*O(x^n)) ; polcoeff( sum(k=0, n, (k%3==0) * polcoeff(A, k) * x^k) / A, n))} /* Michael Somos, Sep 29 2007 */

Formula

Expansion of f(-q^12,-q^15)/f(-q,-q^2) in powers of q where f() is Ramanujan's theta function.

Given A=A0+A1+A2+A3+A4 is the 5-section, then 0= A1^2*A4^2 +2*A2^2*A3^2 -A1*A3^3 -A4*A2^3 -A1*A2*A3*A4.

G.f.: Product_{k>0} (1-x^(27k))(1-x^(27k-12))(1-x^(27k-15))/(1-x^k).

G.f.: 1+ Sum_{k>0} x^k^2 ( Product_{j=1..k-1} 1-x^(3j) )/( (Product_{j=1..2k-1} (1-x^j)) (Product_{j=1..k}(1-x^j)) ).

A104501(n) = A104503(n-1) + A104504(n-2) unless n=0. - Michael Somos, Sep 29 2007

Extensions

Edited by Michael Somos, Mar 15 2006