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.

Previous Showing 31-40 of 40 results.

A136028 Expansion of (phi(q) * phi(q^2))^3 in powers of q where phi() is a Ramanujan theta function.

Original entry on oeis.org

1, 6, 18, 44, 90, 144, 212, 288, 330, 418, 528, 588, 836, 1008, 1056, 1440, 1386, 1356, 1894, 1644, 2064, 2880, 2484, 3168, 3428, 2838, 3696, 3864, 4128, 5040, 5280, 5760, 5418, 5656, 5988, 5376, 7678, 8208, 7572, 10080, 8208, 7788, 10560, 8652, 10404, 13104
Offset: 0

Views

Author

Michael Somos, Dec 10 2007

Keywords

Comments

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

Examples

			G.f. = 1 + 6*q + 18*q^2 + 44*q^3 + 90*q^4 + 144*q^5 + 212*q^6 + 288*q^7 + ...
		

Crossrefs

Programs

  • Magma
    A := Basis( ModularForms( Gamma1(8), 3), 46);  A[1] + 6*A[2] + 18*A[3] + 44*A[4] + 90*A[5] + 144*A[6] + 212*A[7]; /* Michael Somos, Oct 14 2015 */
  • Mathematica
    nmax=60; CoefficientList[Series[Product[((1-x^k)^2 * (1+x^k)^4 * (1+x^(2*k)) / (1+x^(4*k))^2)^3,{k,1,nmax}],{x,0,nmax}],x] (* Vaclav Kotesovec, Oct 14 2015 *)
    a[ n_] := SeriesCoefficient[ (EllipticTheta[ 3, 0, q] EllipticTheta[ 3, 0, q^2])^3, {q, 0, n}]; (* Michael Somos, Oct 14 2015 *)
  • PARI
    {a(n) = my(A); if( n<0, 0, A = x * O(x^n); polcoeff( ((eta(x^2 + A) * eta(x^4 + A))^3 / (eta(x + A) * eta(x^8 + A))^2)^3, n))};
    

Formula

Expansion of (eta(q^2) * eta(q^4))^9 / (eta(q) * eta(q^8))^6 in powers of q.
G.f. is a period 1 Fourier series which satisfies f(-1/(8 t)) = 2^(9/2) (t/i)^3 f(t) where q = exp(2 Pi i t).
G.f.: (Product_{k>0} (1 - x^k)^2 * (1 + x^k)^4 * (1 + x^(2*k)) / (1 + x^(4*k))^2)^3.
a(n) = A029713(n) + 6 * A030207(n). Convolution of A033715 and A097057.
a(n) = A028578(4*n). - Michael Somos, Oct 14 2015

A226240 Expansion of phi(q^4) * phi(q^8) + 2 * q *phi(q^2) * psi(q^8) in powers of q where phi(), psi() are Ramanujan theta functions.

Original entry on oeis.org

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

Views

Author

Michael Somos, Jun 01 2013

Keywords

Comments

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

Examples

			G.f. = 1 + 2*q + 4*q^3 + 2*q^4 + 2*q^8 + 6*q^9 + 4*q^11 + 4*q^12 + 2*q^16 + ...
		

Crossrefs

Programs

  • Magma
    A := Basis( ModularForms( Gamma1(32), 1), 87); A[1] + 2*A[2] + 4*A[4] + 2*A[5] + 2*A[9] + 6*A[10] + 4*A[12] + 4*A[13] + 4*A[16]; /* Michael Somos, Jun 18 2014 */
  • Mathematica
    a[ n_] := SeriesCoefficient[ 1 + 2 Sum[ Boole[ 2 != Mod[ k, 4]] q^k (1 + q^(2 k)) / (1 + q^(4 k)), {k, n}], {q, 0, n}];
  • PARI
    {a(n) = if( n<1, n==0, 2 * (n%4 != 2) * sumdiv( n, d, kronecker( -2, d)))};
    
  • PARI
    {a(n) = local(A, p, e); if( n<1, n==0, A = factor(n); 2 * prod( k= 1, matsize(A)[1], if( p=A[k, 1], e=A[k, 2]; if( p==2, e>1, if( p%8<5, e+1, (1 + (-1)^e) / 2)))))};
    
  • PARI
    {a(n) = local(A); if( n<0, 0, A = x * O(x^n); polcoeff( (eta(x^8 + A) * eta(x^16 + A))^3 / (eta(x^4 + A) * eta(x^32 + A))^2 + 2 * x * eta(x^4 + A)^5 * eta(x^16 + A)^2 / (eta(x^2 + A)^2 * eta(x^8 + A)^3), n))};
    

Formula

Expansion of phi(q) * phi(q^8) + 4 * q^3 * psi(q^8) * psi(q^16) in powers of q where phi(), psi() are Ramanujan theta functions.
a(n) = 2 * b(n) where b(n) is multiplicative and b(2) = 0, b(2^e) = 1 if e>1, b(p^e) = e+1 if p == 1, 3 (mod 8), b(p^e) = (1 + (-1)^e)/2 if p == 5, 7 (mod 8).
G.f.: 1 + 2 * Sum_{k>0 & k !=2 (mod 4)} q^k * (1 + q^(2*k)) / (1 + q^(4*k)).
a(4*n + 2) = 0. a(2*n + 1) = 2 * A113411(n). a(4*n) = A033715(n).
Asymptotic mean: Limit_{m->oo} (1/m) * Sum_{k=1..m} a(k) = 3*Pi/(4*sqrt(2)) = 1.6660811... . - Amiram Eldar, Dec 29 2023

A244554 Expansion of phi(q) * (phi(q) - phi(q^2)) / 2 in powers of q where phi() is a Ramanujan theta function.

Original entry on oeis.org

1, 1, -2, 1, 4, -2, 0, 1, -1, 4, -2, -2, 4, 0, 0, 1, 2, -1, -2, 4, 0, -2, 0, -2, 5, 4, -4, 0, 4, 0, 0, 1, -4, 2, 0, -1, 4, -2, 0, 4, 2, 0, -2, -2, 4, 0, 0, -2, 1, 5, -4, 4, 4, -4, 0, 0, -4, 4, -2, 0, 4, 0, 0, 1, 8, -4, -2, 2, 0, 0, 0, -1, 2, 4, -2, -2, 0, 0
Offset: 1

Views

Author

Michael Somos, Jun 30 2014

Keywords

Comments

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

Examples

			G.f. = q + q^2 - 2*q^3 + q^4 + 4*q^5 - 2*q^6 + q^8 - q^9 + 4*q^10 - 2*q^11 + ...
		

Crossrefs

Programs

  • Magma
    A := Basis( ModularForms( Gamma1(8), 1), 33); A[2] + A[3];
  • Mathematica
    a[ n_] := If[ n < 1, 0, Sum[ {1, 0, -3, 0, 3, 0, -1, 0}[[ Mod[ d, 8, 1] ]], {d, Divisors @ n}]];
    a[ n_] := SeriesCoefficient[ EllipticTheta[ 3, 0, q] (EllipticTheta[ 3, 0, q] - EllipticTheta[ 3, 0, q^2]) / 2, {q, 0, n}];
  • PARI
    {a(n) = if( n<1, 0, sumdiv(n, d, [0, 1, 0, -3, 0, 3, 0, -1][d%8 + 1]))};
    
  • PARI
    {a(n) = my(A); if( n<0, 0, A = sum(k=1, sqrtint(n), 2 * x^k^2, 1 + x * O(x^n)); polcoeff( A * (A - subst(A, x, x^2)) / 2, n))};
    
  • Sage
    A = ModularForms( Gamma1(8), 1, prec=33) . basis(); A[1] + A[2];
    

Formula

Expansion of q * f(-q, -q^7)^2 * phi(q) / psi(-q) = q * f(-q, -q^7)^2 * chi(q)^3 in powers of q where phi(), psi(), f() are Ramanujan theta functions.
Euler transform of period 8 sequence [1, -3, 3, 0, 3, -3, 1, -2, ...].
Moebius transform is period 8 sequence [1, 0, -3, 0, 3, 0, -1, 0, ...].
Convolution product of A244560 and A107635. Convolution product of A000122 and A143259.
a(n) = (A004018(n) - A033715(n)) / 2 = A243747(2*n).
a(2*n) = a(n). a(8*n + 3) = -2 * A033761(n). a(8*n + 5) = 4 * A053692(n). a(8*n + 7) = 0.
Asymptotic mean: Limit_{m->oo} (1/m) * Sum_{k=0..m} a(k) = Pi*(1 - 1/sqrt(2))/2 = 0.460075... . - Amiram Eldar, Jun 08 2025

A245572 Expansion of phi(q) * phi(q^2) + 2 * phi(-q^2) * phi(q^4) in powers of q where phi() is a Ramanujan theta function.

Original entry on oeis.org

3, 2, -2, 4, 6, 0, -4, 0, 6, 6, 0, 4, 12, 0, 0, 0, 6, 4, -6, 4, 0, 0, -4, 0, 12, 2, 0, 8, 0, 0, 0, 0, 6, 8, -4, 0, 18, 0, -4, 0, 0, 4, 0, 4, 12, 0, 0, 0, 12, 2, -2, 8, 0, 0, -8, 0, 0, 8, 0, 4, 0, 0, 0, 0, 6, 0, -8, 4, 12, 0, 0, 0, 18, 4, 0, 4, 12, 0, 0, 0, 0
Offset: 0

Views

Author

Michael Somos, Jul 25 2014

Keywords

Comments

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

Examples

			G.f. = 3 + 2*q - 2*q^2 + 4*q^3 + 6*q^4 - 4*q^6 + 6*q^8 + 6*q^9 + 4*q^11 + ...
		

Crossrefs

Programs

  • Magma
    A := Basis( ModularForms( Gamma1(32), 1), 81);  3*A[1] + 2*A[2] - 2*A[3] + 4*A[4] + 6*A[5] - 4*A[7] + 6*A[9] + 6*A[10] + 4*A[12] + 12*A[13] + 4*A[16];
  • Mathematica
    a[ n_] := SeriesCoefficient[ EllipticTheta[ 3, 0, q] EllipticTheta[ 3, 0, q^2] + 2 EllipticTheta[ 3, 0, -q^2] EllipticTheta[ 3, 0, q^4], {q, 0, n}];
  • PARI
    {a(n) = my(A, p, e); if( n<1, 3*(n==0), A = factor(n); 2 * prod( k=1, matsize(A)[1], [p, e] = A[k, ]; if( p==2, if( e>1, 3, -1), p%8>3, (1 + (-1)^e) / 2, e+1)))};
    
  • PARI
    {a(n) = my(A); if( n<0, 0, A = x * O(x^n); polcoeff( eta(x^2 + A)^3 * eta(x^4 + A)^3 / (eta(x + A)^2 * eta(x^8 + A)^2) + 2 * eta(x^2 + A)^2 * eta(x^8 + A)^5 / (eta(x^4 + A)^3 * eta(x^16 + A)^2), n))};
    

Formula

a(n) = 2 * b(n) where b(n) is multiplicative with b(2) = -1, b(2^e) = 3 if e>1, b(p^e) = e+1 if p == 1, 3 (mod 8), b(p^e) = (1 + (-1)^e)/2 if p == 5, 7 (mod 8).
G.f. is a period 1 Fourier series which satisfies f(-1 / (32 t)) = 4 g(t) where q = exp(2 Pi i t) and g() is the g.f. for A226240.
a(2*n + 1) = 2 * A113411(n). a(4*n) = 3 * A033715(n). a(8*n + 1) = 2 * A112603(n). a(8*n = 3) = 4 * A033761(n). a(8*n + 5) = a(8*n = 7) = 0.

A320069 Expansion of 1/(theta_3(q) * theta_3(q^2)), where theta_3() is the Jacobi theta function.

Original entry on oeis.org

1, -2, 2, -4, 10, -16, 20, -32, 58, -86, 112, -164, 260, -368, 480, -672, 986, -1348, 1750, -2372, 3312, -4416, 5684, -7520, 10148, -13266, 16912, -21960, 28896, -37168, 46944, -60032, 77466, -98312, 123076, -155392, 197422, -247696, 307540, -384096, 481776, -598500
Offset: 0

Views

Author

Seiichi Manyama, Oct 05 2018

Keywords

Crossrefs

Programs

  • Mathematica
    CoefficientList[Series[1/Product[EllipticTheta[3, 0, q^k], {k, 1, 2}], {q, 0, 80}], q] (* G. C. Greubel, Oct 29 2018 *)
  • PARI
    q='q+O('q^80); Vec(1/prod(k=1,2, eta(q^(2*k))^5/(eta(q^k)* eta(q^(4*k)))^2 )) \\ G. C. Greubel, Oct 29 2018

Formula

Convolution inverse of A033715.
a(n) ~ (-1)^n * exp(Pi*sqrt(n)) / (8 * n^(5/4)). - Vaclav Kotesovec, Oct 05 2018

A028572 Expansion of theta_3(z)*theta_3(2z) + theta_2(z)*theta_2(2z) in powers of q^(1/4).

Original entry on oeis.org

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

Views

Author

Keywords

Comments

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

Examples

			1 + 4*x^3 + 2*x^4 + 2*x^8 + 4*x^11 + 4*x^12 + 2*x^16 + 4*x^19 + 4*x^24 + ...
1 + 4*q^(3/4) +2*q +2*q^2 +4*q^(11/4) +4*q^3 +2*q^4 + 4*q^(19/4) +4*q^6 + ...
		

Crossrefs

Programs

  • Mathematica
    terms = 105; max = Sqrt[terms] // Ceiling; s = Sum[x^(3*(n^2 + m^2) + 2*n*m), {n, -max, max}, {m, -max, max}]; CoefficientList[s, x][[1 ;; terms]] (* Jean-François Alcover, Dec 03 2015, using 2nd g.f. *)
  • PARI
    {a(n) = if( n<1, n==0, qfrep( [3, 1; 1, 3], n)[n] * 2)} /* Michael Somos, Nov 20 2006 */
    
  • PARI
    {a(n) = if( n<1, n==0, if( n%4==1 || n%4==2, 0, 2 * sumdiv( n, d, kronecker( -2, d))))} /* Michael Somos, Mar 23 2012 */

Formula

Expansion of phi(x^4) * phi(x^8) + 4 * x^3 * psi(x^8) * psi(x^16) in powers of x where phi(), psi() are Ramanujan theta functions.
G.f. is a period 1 Fourier series which satisfies f(-1 / (32 t)) = 32^(1/2) (t/i) f(t) where q = exp(2 pi i t). - Michael Somos, Mar 23 2012
G.f.: Sum_{n,m} x^(3*(n^2 + m^2) + 2*n*m). - Michael Somos, Nov 20 2006
a(4*n + 1) = a(4*n + 2) = a(8*n + 7) = 0. a(4*n) = A033715(n). a(8*n + 3) = 4 * A033761(n). - Michael Somos, Mar 23 2012

A129438 Expansion of (phi(q) * phi(q^2) + phi(-q^2) * phi(q^4)) / 2 in powers of q where phi() is a Ramanujan theta function.

Original entry on oeis.org

1, 1, 0, 2, 2, 0, 0, 0, 2, 3, 0, 2, 4, 0, 0, 0, 2, 2, 0, 2, 0, 0, 0, 0, 4, 1, 0, 4, 0, 0, 0, 0, 2, 4, 0, 0, 6, 0, 0, 0, 0, 2, 0, 2, 4, 0, 0, 0, 4, 1, 0, 4, 0, 0, 0, 0, 0, 4, 0, 2, 0, 0, 0, 0, 2, 0, 0, 2, 4, 0, 0, 0, 6, 2, 0, 2, 4, 0, 0, 0, 0, 5, 0, 2, 0, 0, 0
Offset: 0

Views

Author

Michael Somos, Apr 14 2007

Keywords

Comments

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

Examples

			G.f. = 1 + q + 2*q^3 + 2*q^4 + 2*q^8 + 3*q^9 + 2*q^11 + 4*q^12 + 2*q^16 + ...
		

Crossrefs

Programs

  • Mathematica
    a[ n_] := SeriesCoefficient[ (EllipticTheta[ 3, 0, q] EllipticTheta[ 3, 0, q^2] + EllipticTheta[ 4, 0, q^2] EllipticTheta[ 3, 0, q^4]) / 2, {q, 0, n}]; (* Michael Somos, Nov 11 2015 *)
  • PARI
    {a(n) = if( n<1, n==0, qfrep([1, 0; 0, 8], n)[n] + qfrep([3, 1; 1, 3], n)[n])};

Formula

Moebius transform is period 32 sequence [1, -1, 1, 2, -1, -1, -1, 0, 1, 1, 1, 2, -1, 1, -1, 0, 1, -1, 1, -2, -1, -1, -1, 0, 1, 1, 1, -2, -1, 1, -1, 0, ...].
a(4*n + 2) = a(8*n + 5) = a(8*n + 7) = 0.
a(n) = A125096(n) unless n=0. a(8*n + 1) = A112603(n). a(8*n + 3) = 2 * A033761(n).
a(2*n + 1) = A113411(n). a(4*n) = A033715(n). - Michael Somos, Nov 11 2015

A320248 Expansion of Product_{k=1..24} theta_3(q^k), where theta_3() is the Jacobi theta function.

Original entry on oeis.org

1, 2, 2, 6, 8, 10, 22, 26, 36, 60, 78, 106, 152, 202, 258, 370, 478, 602, 828, 1042, 1332, 1758, 2198, 2758, 3572, 4446, 5512, 7002, 8614, 10616, 13292, 16260, 19792, 24496, 29724, 35976, 44062, 52992, 63780, 77296, 92518, 110532, 132848, 158036, 187674, 224066, 264960
Offset: 0

Views

Author

Seiichi Manyama, Oct 08 2018

Keywords

Comments

Also the number of integer solutions (a_1, a_2, ... , a_24) to the equation a_1^2 + 2*a_2^2 + ... + 24*a_24^2 = n.
a(24045) = 45676735553670596752038069309732400 and a(24046) = 45676724028345437854371347712212432. So a(24045) > a(24046).

Crossrefs

Product_{k=1..m} theta_3(q^k): A000122 (m=1), A033715 (m=2), A029594 (m=3), A320139 (m=4), A320231 (m=5), A320232 (m=6), A320233 (m=7), A320234 (m=8), A320241 (m=9), A320242 (m=10), A320246 (m=12), A320247 (m=16), this sequence (m=24).
Cf. A320067.

A374294 a(n) is the smallest positive integer k such that A002325(k) = n.

Original entry on oeis.org

1, 3, 9, 27, 81, 99, 729, 297, 1089, 891, 59049, 1683, 531441, 8019, 9801, 5049, 43046721, 18513, 387420489, 15147, 88209, 649539, 31381059609, 31977, 1185921, 5845851, 314721, 136323, 22876792454961, 166617, 205891132094649, 95931, 7144929, 473513931, 10673289, 351747, 150094635296999121
Offset: 1

Views

Author

Seiichi Manyama, Jul 02 2024

Keywords

Examples

			   n |  a(n)
-----+-----------------------
   2 |     3.
   3 |     9 = 3^2.
   4 |    27 = 3^3.
   5 |    81 = 3^4.
   6 |    99 = 3^2 * 11.
   7 |   729 = 3^6.
   8 |   297 = 3^3 * 11.
   9 |  1089 = 3^2 * 11^2.
  10 |   891 = 3^4 * 11.
  11 | 59049 = 3^10.
  12 |  1683 = 3^2 * 11 * 17.
		

Crossrefs

Formula

If p is prime, a(p) = 3^(p-1).
a(n) is divisible by 3 for n > 1.

A306518 Square array A(n,k), n >= 0, k >= 1, read by antidiagonals, where column k is the expansion of Product_{d|k} theta_3(q^d).

Original entry on oeis.org

1, 1, 2, 1, 2, 0, 1, 2, 2, 0, 1, 2, 0, 4, 2, 1, 2, 2, 2, 2, 0, 1, 2, 0, 4, 6, 0, 0, 1, 2, 2, 0, 4, 0, 4, 0, 1, 2, 0, 6, 2, 4, 0, 0, 0, 1, 2, 2, 0, 6, 2, 8, 4, 2, 2, 1, 2, 0, 4, 2, 4, 4, 8, 0, 6, 0, 1, 2, 2, 2, 4, 0, 14, 0, 6, 2, 0, 0, 1, 2, 0, 4, 6, 4, 0, 8, 0, 6, 0, 4, 0, 1, 2, 2, 0, 2, 0, 8, 2, 6, 6, 8, 0, 4, 0
Offset: 0

Views

Author

Ilya Gutkovskiy, Feb 21 2019

Keywords

Examples

			Square array begins:
  1,  1,  1,  1,  1,  1,  ...
  2,  2,  2,  2,  2,  2,  ...
  0,  2,  0,  2,  0,  2,  ...
  0,  4,  2,  4,  0,  6,  ...
  2,  2,  6,  4,  2,  6,  ...
  0,  0,  0,  4,  2,  4,  ...
		

Crossrefs

Programs

  • Mathematica
    Table[Function[k, SeriesCoefficient[Product[EllipticTheta[3, 0, q^d], {d, Divisors[k]}], {q, 0, n}]][i - n + 1], {i, 0, 13}, {n, 0, i}] // Flatten

Formula

G.f. of column k: Product_{d|k} theta_3(q^d).
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