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 11-20 of 25 results. Next

A001940 Absolute value of coefficients of an elliptic function.

Original entry on oeis.org

1, 6, 27, 98, 309, 882, 2330, 5784, 13644, 30826, 67107, 141444, 289746, 578646, 1129527, 2159774, 4052721, 7474806, 13569463, 24274716, 42838245, 74644794, 128533884, 218881098, 368859591, 615513678, 1017596115, 1667593666, 2710062756, 4369417452
Offset: 0

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Author

Keywords

References

  • A. Cayley, A memoir on the transformation of elliptic functions, Collected Mathematical Papers. Vols. 1-13, Cambridge Univ. Press, London, 1889-1897, Vol. 9, p. 128.
  • N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
  • N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Crossrefs

Programs

  • Mathematica
    nn = 4*10; b = Flatten[Table[{6, 6, 6, 0}, {nn/4}]]; CoefficientList[x*Series[Product[1/(1 - x^m)^b[[m]], {m, nn}], {x, 0, nn}], x] (* T. D. Noe, Aug 17 2012 *)
    nmax = 40; CoefficientList[Series[Product[((1 - x^(4*k)) / (1 - x^k))^6, {k, 1, nmax}], {x, 0, nmax}], x] (* Vaclav Kotesovec, Nov 15 2017 *)

Formula

G.f.: Product ( 1 - x^k )^(-c(k)), c(k) = 6, 6, 6, 0, 6, 6, 6, 0, ....
a(n) ~ 3^(1/4) * exp(sqrt(3*n)*Pi) / (128*sqrt(2)*n^(3/4)). - Vaclav Kotesovec, Nov 15 2017
G.f.: Product_{k>=1} ((1 + x^(2*k))/(1 - x^(2*k-1)))^6. - Ilya Gutkovskiy, Dec 04 2017

Extensions

Extended and corrected by Simon Plouffe

A001941 Absolute values of coefficients of an elliptic function.

Original entry on oeis.org

1, 7, 35, 140, 483, 1498, 4277, 11425, 28889, 69734, 161735, 362271, 786877, 1662927, 3428770, 6913760, 13660346, 26492361, 50504755, 94766875, 175221109, 319564227, 575387295, 1023624280, 1800577849, 3133695747, 5399228149, 9214458260, 15584195428
Offset: 0

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Author

Keywords

References

  • A. Cayley, A memoir on the transformation of elliptic functions, Collected Mathematical Papers. Vols. 1-13, Cambridge Univ. Press, London, 1889-1897, Vol. 9, p. 128.
  • N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
  • N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Crossrefs

Programs

  • Mathematica
    nn = 4*10; b = Flatten[Table[{7, 7, 7, 0}, {nn/4}]]; CoefficientList[x*Series[Product[1/(1 - x^m)^b[[m]], {m, nn}], {x, 0, nn}], x] (* T. D. Noe, Aug 17 2012 *)
    nmax = 40; CoefficientList[Series[Product[((1 - x^(4*k)) / (1 - x^k))^7, {k, 1, nmax}], {x, 0, nmax}], x] (* Vaclav Kotesovec, Nov 15 2017 *)

Formula

G.f.: Product ( 1 - x^k )^-c(k), c(k) = 7, 7, 7, 0, 7, 7, 7, 0, ....
a(n) ~ 7^(1/4) * exp(sqrt(7*n/2)*Pi) / (256*2^(3/4)*n^(3/4)). - Vaclav Kotesovec, Nov 15 2017
G.f.: Product_{k>=1} ((1 + x^(2*k))/(1 - x^(2*k-1)))^7. - Ilya Gutkovskiy, Dec 04 2017

A263002 Expansion of (f(-x^5) / f(-x))^2 in powers of x where f() is a Ramanujan theta function.

Original entry on oeis.org

1, 2, 5, 10, 20, 34, 61, 100, 165, 260, 408, 620, 940, 1390, 2045, 2960, 4257, 6040, 8525, 11900, 16522, 22738, 31130, 42300, 57210, 76872, 102834, 136800, 181230, 238900, 313725, 410160, 534330, 693330, 896655, 1155420, 1484274, 1900420, 2426215, 3088100
Offset: 0

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Author

Michael Somos, Oct 07 2015

Keywords

Comments

Ramanujan theta functions: f(q) (see A121373), phi(q) (A000122), psi(q) (A010054), chi(q) (A000700).
Number of 5-regular bipartitions of n. - N. J. A. Sloane, Oct 20 2019

Examples

			G.f. = 1 + 2*x + 5*x^2 + 10*x^3 + 20*x^4 + 34*x^5 + 61*x^6 + 100*x^7 + ...
G.f. = q + 2*q^4 + 5*q^7 + 10*q^10 + 20*q^13 + 34*q^16 + 61*q^19 + 100*q^22 + ...
		

References

  • Kathiravan, T., and S. N. Fathima. "On L-regular bipartitions modulo L." The Ramanujan Journal 44.3 (2017): 549-558.

Crossrefs

Cf. A058511.
Number of r-regular bipartitions of n for r = 2,3,4,5,6: A022567, A328547, A001936, A263002, A328548.

Programs

  • Maple
    f:=(k,M) -> mul(1-q^(k*j),j=1..M);
    LRBP := (L,M) -> (f(L,M)/f(1,M))^2;
    S := L -> seriestolist(series(LRBP(L,80),q,60));
    S(5); # N. J. A. Sloane, Oct 20 2019
  • Mathematica
    a[ n_] := SeriesCoefficient[ (QPochhammer[ x^5] / QPochhammer[ x])^2, {x, 0, n}];
  • PARI
    {a(n) = my(A); if( n<0, 0, A = x * O(x^n); polcoeff( (eta(x^5 + A) / eta(x + A))^2, n))};

Formula

Expansion of q^(-1/3) * (eta(q^5) / eta(q))^2 in powers of q.
Euler transform of period 5 sequence [ 2, 2, 2, 2, 0, ...].
G.f. is a period 1 Fourier series which satisfies f(-1 / (45 t)) = (1/5) g(t) where q = exp(2 Pi i t) and g() is the g.f. of A058511.
Given g.f. A(x), then B(q) = q * A(q^3) satisfies 0 = f(B(q), B(q^2)) where f(u, v) = (u - v^2) * (v - u^2) - 4*u^2*v^2.
Convolution inverse is A058511.
a(n) ~ exp(4*Pi*sqrt(n/15)) / (sqrt(2) * 3^(1/4) * 5^(5/4) * n^(3/4)). - Vaclav Kotesovec, Oct 14 2015
See Maple code for a simple g.f. - N. J. A. Sloane, Oct 20 2019

A333374 G.f.: Sum_{k>=1} (x^(k*(k+1)) * Product_{j=1..k} (1 + x^j)/(1 - x^j)).

Original entry on oeis.org

1, 0, 1, 2, 2, 2, 3, 4, 6, 8, 10, 12, 15, 18, 22, 28, 34, 42, 52, 62, 75, 90, 106, 126, 150, 176, 208, 246, 288, 338, 397, 462, 538, 626, 724, 838, 968, 1114, 1282, 1474, 1690, 1936, 2217, 2532, 2890, 3296, 3750, 4264, 4844, 5492, 6222, 7042, 7958, 8986, 10138
Offset: 0

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Author

Vaclav Kotesovec, Mar 17 2020

Keywords

Comments

The g.f. Sum_{k >= 1} x^(k*(k+1)) * Product_{j = 1..k} (1 + x^j)/(1 - x^j) = Sum_{k >= 1} x^(k*(k+1)) * Product_{j = 1..k} (1 + x^j)/(1 - x^j + 2*x^j) == Sum_{k >= 1} x^(k*(k+1)) (mod 2). It follows that a(n) is odd iff n = k*(k + 1) for some nonnegative integer k. - Peter Bala, Jan 04 2025

Crossrefs

Programs

  • Mathematica
    nmax = 100; CoefficientList[Series[Sum[x^(n*(n+1))*Product[(1+x^k)/(1-x^k), {k, 1, n}], {n, 0, Sqrt[nmax]}], {x, 0, nmax}], x]
    nmax = 100; p = 1; s = 1; Do[p = Normal[Series[p*(1 + x^k)/(1 - x^k)*x^(2*k), {x, 0, nmax}]]; s += p;, {k, 1, Sqrt[nmax]}]; Take[CoefficientList[s, x], nmax + 1]

Formula

Limit_{n->infinity} A066447(n) / a(n) = A058265 = (1 + (19+3*sqrt(33))^(1/3) + (19-3*sqrt(33))^(1/3))/3 = 1.839286755214... (the tribonacci constant).
Compare with: A306734(n) / A333179(n) -> A060006 (the plastic constant) and A003114(n) / A003106(n) -> A001622 (golden ratio).
a(n) ~ c * d^sqrt(n) / n^(3/4), where d = A376841 = 7.1578741786143524880205... = exp(2*sqrt(log(r)^2 - polylog(2, -r^2) + polylog(2, r^2))) and c = 0.10511708841962944170826735560432... = (log(r)^2 - polylog(2, -r^2) + polylog(2, r^2))^(1/4) * sqrt(1/24 - sinh(arcsinh(sqrt(11)/4)/3) / (12*sqrt(11))) / sqrt(Pi), where r = A192918 = 0.54368901269207636157... is the real root of the equation r^2*(1+r) = 1-r. - Vaclav Kotesovec, Mar 17 2020, updated Oct 10 2024

A127391 Series expansion of the elliptic function sqrt(k) = theta_2/theta_3 in powers of q^(1/4).

Original entry on oeis.org

0, 2, 0, 0, 0, -4, 0, 0, 0, 10, 0, 0, 0, -20, 0, 0, 0, 36, 0, 0, 0, -64, 0, 0, 0, 110, 0, 0, 0, -180, 0, 0, 0, 288, 0, 0, 0, -452, 0, 0, 0, 692, 0, 0, 0, -1044, 0, 0, 0, 1554, 0, 0, 0, -2276, 0, 0, 0, 3296, 0, 0, 0, -4724, 0, 0, 0, 6696, 0, 0, 0, -9408, 0, 0, 0, 13108, 0, 0, 0, -18112, 0, 0, 0, 24850, 0
Offset: 0

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Author

N. J. A. Sloane, Mar 31 2007

Keywords

Comments

It appears that a(n) = 2 * A208933(n) - A212318(n) for n>0. - Thomas Baruchel, May 14 2018
Empirical: Sum_{n>=1} a(n)/exp(Pi*(n-1)) = 3 + 2*sqrt(2) - 2*sqrt(4 + 3*sqrt(2)). - Simon Plouffe, Mar 01 2021

Examples

			2*x - 4*x^5 + 10*x^9 - 20*x^13 + 36*x^17 - 64*x^21 + 110*x^25 -180*x^29 + ...
2*q^(1/4) - 4*q^(5/4) + 10*q^(9/4) - 20*q^(13/4) + 36*q^(17/4) - 64*q^(21/4) + ...
		

References

  • N. J. Fine, Basic Hypergeometric Series and Applications, Amer. Math. Soc., 1988; Eq. (34.3).

Crossrefs

See A127392 for another version. Dividing by 2 gives A079006. Cf. A001936, A001938.

A127392 Expansion of the elliptic function sqrt(k(q))/q^(1/4) in powers of q, where sqrt(k(q)) = theta_2(q)/theta_3(q).

Original entry on oeis.org

2, -4, 10, -20, 36, -64, 110, -180, 288, -452, 692, -1044, 1554, -2276, 3296, -4724, 6696, -9408, 13108, -18112, 24850, -33864, 45844, -61696, 82564, -109892, 145536, -191828, 251684, -328804, 427802, -554408, 715808, -920896, 1180660, -1508736, 1921896, -2440740, 3090612
Offset: 0

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Author

N. J. A. Sloane, Mar 31 2007

Keywords

Examples

			2 - 4*x + 10*x^2 - 20*x^3 + 36*x^4 - 64*x^5 + 110*x^6 - 180*x^7 + 288*x^8 - ...
2*q^(1/4) - 4*q^(5/4) + 10*q^(9/4) - 20*q^(13/4) + 36*q^(17/4) - 64*q^(21/4) + ...
		

References

  • N. J. Fine, Basic Hypergeometric Series and Applications, Amer. Math. Soc., 1988; Eq. (34.3).

Crossrefs

See A127391 for another version. Dividing by 2 gives A079006. Cf. A001936, A001938.

Programs

  • Mathematica
    QP = QPochhammer; s = 2*(QP[q]*(QP[q^4]^2/QP[q^2]^3))^2 + O[q]^40; CoefficientList[s, q] (* Jean-François Alcover, Nov 27 2015, adapted from PARI *)
    nmax = 50; CoefficientList[Series[2*Product[(1+x^(2*k))^4 / (1+x^k)^2, {k, 1, nmax}], {x, 0, nmax}], x] (* Vaclav Kotesovec, Jul 04 2016 *)
  • PARI
    {a(n) = local(A); if( n<0, 0, A = x * O(x^n); polcoeff( 2 * (eta(x + A) * eta(x^4 + A)^2 / eta(x^2 + A)^3)^2, n))} /* Michael Somos, Jun 12 2012 */

Formula

Expansion of 2 * q^(-1/4) * (eta(q) * eta(q^4)^2 / eta(q^2)^3)^2 in powers of q. - Michael Somos, Jun 12 2012
a(n) ~ (-1)^n * exp(Pi*sqrt(n))/(2^(5/2)*n^(3/4)). - Vaclav Kotesovec, Jul 04 2016
2 * ({1} U (Euler transform of period 4 sequence [-2, 4, -2, 0])). - Georg Fischer, Dec 06 2022

A187154 Expansion of psi(x^4) / phi(-x) in powers of x where phi(), psi() are Ramanujan theta functions.

Original entry on oeis.org

1, 2, 4, 8, 15, 26, 44, 72, 114, 178, 272, 408, 605, 884, 1276, 1824, 2580, 3616, 5028, 6936, 9498, 12922, 17468, 23472, 31369, 41700, 55156, 72616, 95172, 124202, 161436, 209016, 269616, 346562, 443952, 566856, 721530, 915642, 1158608, 1461968, 1839789
Offset: 0

Views

Author

Michael Somos, Mar 08 2011

Keywords

Comments

Ramanujan theta functions: f(q) (see A121373), phi(q) (A000122), psi(q) (A010054), chi(q) (A000700).
Since phi(-x) = 1 + 2*Sum_{k >= 1} (-1)^k*x^(k^2) == 1 (mod 2), it follows that the g.f. psi(x^4) / phi(-x) == psi(x^4) == Sum_{k >= 0} x^(2*k*(k+1)) (mod 2). Hence a(n) is odd iff n = 2*k*(k + 1) for some nonnegative integer k. - Peter Bala, Jan 07 2025

Examples

			1 + 2*x + 4*x^2 + 8*x^3 + 15*x^4 + 26*x^5 + 44*x^6 + 72*x^7 + 114*x^8 + ...
q + 2*q^3 + 4*q^5 + 8*q^7 + 15*q^9 + 26*q^11 + 44*q^13 + 72*q^15 + 114*q^17 + ...
		

Crossrefs

Programs

  • Mathematica
    nmax = 50; CoefficientList[Series[Product[(1 + x^k)^2 * (1 + x^(2*k)) * (1 + x^(4*k))^2, {k, 1, nmax}], {x, 0, nmax}], x] (* Vaclav Kotesovec, Sep 10 2015 *)
    a[n_]:= SeriesCoefficient[EllipticTheta[2, 0, q^2]/(2*Sqrt[q]* EllipticTheta[3, 0, -q]), {q, 0, n}]; Table[A187154[n], {n, 0, 50}] (* G. C. Greubel, Dec 04 2017 *)
  • PARI
    {a(n) = local(A); if( n<0, 0, A = x * O(x^n); polcoeff( eta(x^2 + A) * eta(x^8 + A)^2 / (eta(x + A)^2 * eta(x^4 + A)), n))}

Formula

Expansion of q^(-1/2) * eta(q^2) * eta(q^8)^2 / (eta(q)^2 * eta(q^4)) in powers of q.
Euler transform of period 8 sequence [ 2, 1, 2, 2, 2, 1, 2, 0, ...].
G.f. is a period 1 Fourier series which satisfies f(-1 / (32 t)) = 32^(-1/2) g(t) where q = exp(2 Pi i t) and g() is g.f. for A093085.
Convolution inverse of A093085. Convolution square is A107035.
a(n) ~ exp(sqrt(n)*Pi)/(16*n^(3/4)). - Vaclav Kotesovec, Sep 10 2015

A328547 Number of 3-regular bipartitions of n.

Original entry on oeis.org

1, 2, 5, 8, 16, 26, 44, 68, 108, 162, 245, 356, 521, 740, 1053, 1468, 2045, 2804, 3836, 5184, 6988, 9326, 12409, 16376, 21546, 28154, 36674, 47492, 61317, 78764, 100880, 128628, 163553, 207134, 261630, 329288, 413395, 517316, 645803, 803844, 998282
Offset: 0

Views

Author

N. J. A. Sloane, Oct 19 2019

Keywords

References

  • Kathiravan, T., and S. N. Fathima. "On L-regular bipartitions modulo L." The Ramanujan Journal 44.3 (2017): 549-558.

Crossrefs

Number of r-regular bipartitions of n for r = 2,3,4,5,6: A022567, A328547, A001936, A263002, A328548.
Cf. A000726.

Programs

  • Maple
    f:=(k,M) -> mul(1-q^(k*j),j=1..M);
    LRBP := (L,M) -> (f(L,M)/f(1,M))^2;
    S := L -> seriestolist(series(LRBP(L,80),q,60));
    S(3);
  • Mathematica
    nmax = 40; CoefficientList[Series[Product[1 + x^j + x^(2*j), {j, 1, nmax}]^2, {x, 0, nmax}], x] (* Vaclav Kotesovec, Oct 08 2024 *)

Formula

a(n) ~ exp(Pi*sqrt(8*n)/3) / (2^(3/4) * 3^(3/2) * n^(3/4)). - Vaclav Kotesovec, Oct 08 2024

A328548 Number of 6-regular bipartitions of n.

Original entry on oeis.org

1, 2, 5, 10, 20, 36, 63, 106, 175, 280, 441, 680, 1034, 1548, 2290, 3346, 4840, 6930, 9837, 13844, 19337, 26810, 36925, 50530, 68741, 92984, 125113, 167490, 223155, 295960, 390825, 513954, 673214, 878480, 1142190, 1479892, 1911051, 2459896, 3156602
Offset: 0

Views

Author

N. J. A. Sloane, Oct 19 2019

Keywords

References

  • Kathiravan, T., and S. N. Fathima. "On L-regular bipartitions modulo L." The Ramanujan Journal 44.3 (2017): 549-558.

Crossrefs

Number of r-regular bipartitions of n for r = 2,3,4,5,6: A022567, A328547, A001936, A263002, A328548.
Cf. A219601.

Programs

  • Maple
    f:=(k,M) -> mul(1-q^(k*j),j=1..M);
    LRBP := (L,M) -> (f(L,M)/f(1,M))^2;
    S := L -> seriestolist(series(LRBP(L,80),q,60));
    S(6);
  • Mathematica
    nmax = 40; CoefficientList[Series[Product[(1 - x^(6*k))/(1 - x^k), {k, 1, nmax}]^2, {x, 0, nmax}], x] (* Vaclav Kotesovec, Oct 08 2024 *)

Formula

a(n) ~ 5^(1/4) * exp(Pi*sqrt(10*n)/3) / (2^(9/4) * 3^(3/2) * n^(3/4)). - Vaclav Kotesovec, Oct 08 2024

A082304 McKay-Thompson series of class 16d for the Monster group.

Original entry on oeis.org

1, -2, -1, 2, 3, -2, -4, 4, 5, -8, -8, 10, 11, -12, -15, 18, 22, -26, -29, 34, 38, -42, -51, 56, 66, -78, -85, 98, 109, -120, -139, 156, 176, -202, -222, 250, 279, -306, -346, 384, 429, -482, -530, 590, 650, -714, -797, 876, 972, -1080, -1180, 1304, 1431, -1562, -1728, 1892, 2078, -2290, -2496
Offset: 0

Views

Author

Michael Somos, Apr 08 2003

Keywords

Comments

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

Examples

			T16d = 1/q - 2*q^3 - q^7 + 2*q^11 + 3*q^15 - 2*q^19 - 4*q^23 + 4*q^27 + ...
		

Crossrefs

Programs

  • Mathematica
    a[ n_] := SeriesCoefficient[ (QPochhammer[ x] / QPochhammer[ x^4])^2, {x, 0, n}]; (* Michael Somos, Jul 04 2014 *)
  • PARI
    {a(n) = local(A); if( n<0, 0, A = x * O(x^n); polcoeff( (eta(x + A) / eta(x^4 + A))^2, n))};

Formula

Expansion of phi(-q) / psi(q^2) in powers of q where phi(), psi() are Ramanujan theta functions.
Expansion of q^(1/4) * (eta(q) / eta(q^4))^2 in powers of q.
Euler transform of period 4 sequence [ -2, -2, -2, 0, ...].
G.f. is a period 1 Fourier series which satisfies f(-1 / (64 t)) = 4 g(t) where q = exp(2 Pi i t) and g() is the g.f. for A001936. - Michael Somos, Jul 04 2014
Given g.f. A(x), then B(q) = A(q)^4 / q satisfies 0 = f(B(q), B(q^2)) where f(u, v) = v^2 - u * (16 + u) * (16 + v). - Michael Somos, Jul 04 2014
Given g.f. A(x), then B(q) = A(q^4) / q satisfies 0 = f(B(q), B(q^3)) where f(u, v) = (u^2 + v^2)^2 - u*v * (4 + u*v)^2. - Michael Somos, Aug 13 2007
Given g.f. A(x), then B(q) = A(q^4) / q satisfies 0 = f(B(q), B(q^5)) where f(u, v) = u*v * (16 + u^2*v^2)^2 - (u+v)^2 * (u^2 - 6*u*v + v^2)^2. - Michael Somos, Jul 04 2014
G.f.: Product_{k>0} ((1 - x^k) / (1 - x^(4*k)))^2.
a(n) = (-1)^n * A029839(n). Convolution inverse of A001936. - Michael Somos, Jul 04 2014
abs(a(n)) ~ exp(Pi*sqrt(n)/2) / (2^(3/2) * n^(3/4)). - Vaclav Kotesovec, Feb 07 2023
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