cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

Showing 1-4 of 4 results.

A028609 Expansion of (theta_3(z)*theta_3(11z) + theta_2(z)*theta_2(11z)).

Original entry on oeis.org

1, 2, 0, 4, 2, 4, 0, 0, 0, 6, 0, 2, 4, 0, 0, 8, 2, 0, 0, 0, 4, 0, 0, 4, 0, 6, 0, 8, 0, 0, 0, 4, 0, 4, 0, 0, 6, 4, 0, 0, 0, 0, 0, 0, 2, 12, 0, 4, 4, 2, 0, 0, 0, 4, 0, 4, 0, 0, 0, 4, 8, 0, 0, 0, 2, 0, 0, 4, 0, 8, 0, 4, 0, 0, 0, 12, 0, 0, 0, 0, 4, 10, 0, 0, 0, 0, 0, 0, 0, 4, 0, 0, 4, 8, 0, 0, 0, 4, 0, 6, 6, 0, 0
Offset: 0

Views

Author

N. J. A. Sloane

Keywords

Comments

Theta series of lattice with Gram matrix [2, 1; 1, 6].
Number of integer solutions (x, y) to x^2 + x*y + 3*y^2 = n. - Michael Somos, Sep 20 2004
Ramanujan theta functions: f(q) (see A121373), phi(q) (A000122), psi(q) (A010054), chi(q) (A000700).

Examples

			G.f. = 1 + 2*x + 4*x^3 + 2*x^4 + 4*x^5 + 6*x^9 + 2*x^11 + 4*x^12 + 8*x^15 + ...
Theta series of lattice with Gram matrix [2, 1; 1, 6] = 1 + 2*q^2 + 4*q^6 + 2*q^8 + 4*q^10 + 6*q^18 + 2*q^22 + 4*q^24 + 8*q^30 + 2*q^32 + 4*q^40 + 4*q^46 + 6*q^50 + 8*q^54 + 4*q^62 + 4*q^66 + 6*q^72 + 4*q^74 + ...

References

  • Henry McKean and Victor Moll, Elliptic Curves, Cambridge University Press, 1997, page 202. MR1471703 (98g:14032).

Links

Crossrefs

Cf. A028610, A035179, A028954, A056874.
Cf. A000122, A000700, A010054, A121373.
Number of integer solutions to f(x,y) = n where f(x,y) is the principal binary quadratic form with discriminant d: A004016 (d=-3), A004018 (d=-4), A002652 (d=-7), A033715 (d=-8), this sequence (d=-11), A028641 (d=-19), A138811 (d=-43).

Programs

  • Magma
    A := Basis( ModularForms( Gamma1(11), 1), 103); A[1] + 2*A[2] + 4*A[4] + 2*A[5]; /* Michael Somos, Jul 12 2014 */
  • Mathematica
    a[ n_] := If[ n < 1, Boole[ n == 0], DivisorSum[ n, KroneckerSymbol[ -11, #] &] 2]; (* Michael Somos, Jul 12 2014 *)
a[ n_] := SeriesCoefficient[ EllipticTheta[ 3, 0, q] EllipticTheta[ 3, 0, q^11] + EllipticTheta[ 2, 0, q] EllipticTheta[ 2, 0, q^11], {q, 0, n}]; (* Michael Somos, Jul 12 2014 *)
  • PARI
    {a(n) = my(t); if( n<1, n==0, 2 * issquare(n) + 2 * sum( y=1, sqrtint(n * 4\11), 2 * issquare( t=4*n - 11*y^2) - (t==0)))}; /* Michael Somos, Sep 20 2004 */
  • PARI
    {a(n) = if( n<0, 0, polcoeff( 1 + 2 * x * Ser(qfrep( [ 2, 1; 1, 6], n, 1)), n))}; /* Michael Somos, Apr 21 2015 */
  • PARI
    {a(n) = if( n<1, n==0, direuler( p=2, n, 1 / (1 - X) / (1 - kronecker( -11, p) * X))[n] * 2)}; /* Michael Somos, Jun 05 2005 */
  • PARI
    {a(n) = if( n<1, n==0, 2 * sumdiv( n, d, kronecker( -11, d)))}; /* Michael Somos, Jan 29 2007 */

Formula

Expansion of phi(x) * phi(x^11) = 4 * x^3 * psi(x^2) * psi(x^22) in powers of x where phi(), psi() are Ramanujan theta functions. - Michael Somos, Apr 21 2015
From Michael Somos, Jan 29 2007: (Start)
Moebius transform is period 11 sequence [ 2, -2, 2, 2, 2, -2, -2, -2, 2, -2, 0, ...].
a(n) = 2 * b(n) and b(n) is multiplicative with b(11^e) = 1, b(p^e) = (1 + (-1)^e) / 2 if p == 2, 6, 7, 8, 10 (mod 11), b(p^e) = e + 1 if p == 1, 3, 4, 5, 9 (mod 11).
G.f.: 1 + 2 * Sum_{k>0} Kronecker( -11, k) * x^k / (1 - x^k). (End)
G.f. is a period 1 Fourier series which satisfies f(-1 / (11 t)) = 11^(1/2) (t/i) f(t) where q = exp(2 Pi i t). - Michael Somos, Jun 05 2007
Expansion of (F(x)^2 + 4 * F(x^2)^2 + 8 * F(x^4)^2) / F(x^2) in powers of x or expansion of (F(x)^2 + 2 * F(x^2)^2 + 2 * F(x^4)^2) / F(x^2) in powers of x^4 where F(x) = x^(1/2) * f(-x) * f(-x^11) and f() is a Ramanujan theta function. - Michael Somos, Mar 01 2010
a(n) = 2 * A035179(n) unless n=0. Convolution square is A028610.
Asymptotic mean: Limit_{m->oo} (1/m) * Sum_{k=0..m} a(k) = 2*Pi/sqrt(11) = 1.894451... . - Amiram Eldar, Dec 16 2023

A032442 Expansion of 1 / Product_{k >= 1} (1-q^k)^2*(1-q^(11k))^2.

Original entry on oeis.org

1, 2, 5, 10, 20, 36, 65, 110, 185, 300, 481, 754, 1169, 1780, 2685, 3996, 5894, 8600, 12450, 17860, 25442, 35964, 50519, 70490, 97800, 134892, 185099, 252664, 343280, 464200, 625033, 837998, 1119114, 1488720, 1973210, 2606028, 3430238, 4500224, 5885540
Offset: 0

Views

Author

N. J. A. Sloane

Keywords

Comments

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

Examples

			G.f. = 1 + 2*x + 5*x^2 + 10*x^3 + 20*x^4 + 36*x^5 + 65*x^6 + 110*x^7 + ...
G.f. = 1/q + 2 + 5*q + 10*q^2 + 20*q^3 + 36*q^4 + 65*q^5 + 110*q^6 + ...

Links

Crossrefs

Cf. A006571, A028610, A128525.

Programs

  • Mathematica
    a[ n_] := SeriesCoefficient[ (QPochhammer[ x] QPochhammer[ x^11])^-2, {x, 0, n}]; (* Michael Somos, Apr 21 2015 *)
nmax=60; CoefficientList[Series[Product[1/((1-x^k)^2 * (1-x^(11*k))^2),{k,1,nmax}],{x,0,nmax}],x] (* Vaclav Kotesovec, Oct 13 2015 *)
  • PARI
    {a(n) = my(A); if( n<0, 0, A = x * O(x^n); polcoeff( (eta(x + A) * eta(x^11 + A))^-2, n))}; /* Michael Somos, Apr 21 2015 */

Formula

Expansion of 1 / (f(-x) * f(-x^11))^2 in powers of x where f() is a Ramanujan theta function. - Michael Somos, Apr 21 2015
Expansion of q / eta(q)^2 * eta(q^11)^2 in powers of q. - Michael Somos, Apr 21 2015
Euler transform of period 11 sequence [ 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 4, ...]. - Michael Somos, Apr 21 2015
Given g.f. A(x), then B(q) = A(q)/q satisfies 0 = f(B(q), B(q^2), B(q^4)) where f(u, v, w) = u^2 * (w^2 + 16*v^2) - v^2 * (v + 4*u) * (w + 4*u). - Michael Somos, Apr 21 2015
G.f. is a period 1 Fourier series which satisfies f(-1 / (11 t)) = 11^-1 (t/i)^-2 f(t) where q = exp(2 Pi i t). - Michael Somos, Apr 21 2015
G.f.: (Product_{k > 0} (1 - x^k)^2 * (1 - x^(11*k)))^-2.
Convolution inverse of A006571. Convolution with A028610 is A128525. - Michael Somos, Apr 21 2015
a(n) ~ exp(4*Pi*sqrt(n/11)) / (sqrt(2) * 11^(1/4) * n^(7/4)). - Vaclav Kotesovec, Oct 13 2015

A028611 Expansion of (theta_3(z)*theta_3(11z) + theta_2(z)*theta_2(11z))^3.

Original entry on oeis.org

1, 6, 12, 20, 54, 84, 120, 192, 204, 346, 312, 414, 380, 672, 480, 880, 726, 1152, 1092, 1440, 1116, 1920, 1332, 1860, 2040, 2106, 1680, 2640, 2496, 3360, 3120, 3108, 3276, 4580, 2880, 4992, 4114, 4500, 3600, 6720, 5304, 6720, 4800, 7392, 5646, 7844, 6360, 7500
Offset: 0

Views

Author

N. J. A. Sloane

Keywords

Links

Crossrefs

Cf. A028609, A028610, A028612.

Programs

  • PARI
    a(n) = polcoeff((1 + 2*x*Ser(qfrep([2, 1; 1, 6], n, 1)))^3, n); \\ Jinyuan Wang, Feb 20 2020

Extensions

More terms from Jinyuan Wang, Feb 20 2020

A028612 Expansion of (theta_3(z)*theta_3(11z) + theta_2(z)*theta_2(11z))^4.

Original entry on oeis.org

1, 8, 24, 48, 120, 256, 416, 736, 1112, 1624, 2384, 2792, 3904, 4560, 6080, 6352, 9176, 9296, 13688, 13728, 18352, 19168, 25656, 23632, 32992, 31400, 38800, 39664, 49024, 48400, 61632, 58512, 73368, 80112, 86832, 84768, 108472, 99808, 122784, 122240, 143504, 137200
Offset: 0

Views

Author

N. J. A. Sloane

Keywords

Links

Crossrefs

Cf. A028609, A028610, A028611.

Programs

  • PARI
    a(n) = polcoeff((1 + 2*x*Ser(qfrep([2, 1; 1, 6], n, 1)))^4, n); \\ Jinyuan Wang, Feb 20 2020

Extensions

More terms from Jinyuan Wang, Feb 20 2020
Showing 1-4 of 4 results.

Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

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