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 1-7 of 7 results.

A002107 Expansion of Product_{k>=1} (1 - x^k)^2.

Original entry on oeis.org

1, -2, -1, 2, 1, 2, -2, 0, -2, -2, 1, 0, 0, 2, 3, -2, 2, 0, 0, -2, -2, 0, 0, -2, -1, 0, 2, 2, -2, 2, 1, 2, 0, 2, -2, -2, 2, 0, -2, 0, -4, 0, 0, 0, 1, -2, 0, 0, 2, 0, 2, 2, 1, -2, 0, 2, 2, 0, 0, -2, 0, -2, 0, -2, 2, 0, -4, 0, 0, -2, -1, 2, 0, 2, 0, 0, 0, -2
Offset: 0

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Author

Keywords

Comments

Number of partitions of n into an even number of distinct parts minus number of partitions of n into an odd number of distinct parts, with 2 types of each part. E.g., for n=4, we consider k and k* to be different versions of k and so we have 4, 4*, 31, 31*, 3*1, 3*1*, 22*, 211*, 2*11*. The even partitions number 5 and the odd partitions number 4, so a(4)=5-4=1. - Jon Perry, Apr 04 2004
Also, number of partitions of n into parts of -2 different kinds (based upon formal analogy). - Michele Dondi (blazar(AT)lcm.mi.infn.it), Jun 29 2004
Ramanujan theta functions: f(q) (see A121373), phi(q) (A000122), psi(q) (A010054), chi(q) (A000700).
Number 68 of the 74 eta-quotients listed in Table I of Martin (1996).

Examples

			G.f. = 1 - 2*x - x^2 + 2*x^3 + x^4 + 2*x^5 - 2*x^6 - 2*x^8 - 2*x^9 + x^10 + ...
G.f. = q - 2*q^13 - q^25 + 2*q^37 + q^49 + 2*q^61 - 2*q^73 - 2*q^97 - 2*q^109 + ...
		

References

  • 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

Cf. A000712 (reciprocal of g.f.), A010815, A010816, A258406.
Powers of Euler's product: A000594, A000727 - A000731, A000735, A000739, A010815 - A010840.

Programs

  • Julia
    # DedekindEta is defined in A000594.
    A002107List(len) = DedekindEta(len, 2)
    A002107List(78) |> println # Peter Luschny, Mar 09 2018
  • Magma
    Basis( CuspForms( Gamma1(144), 1), 926) [1]; /* Michael Somos, May 17 2015 */
    
  • Maple
    A010816 := proc (n); if frac(sqrt(8*n+1)) = 0 then (-1)^((1/2)*isqrt(8*n+1)-1/2)*isqrt(8*n+1) else 0 end if; end proc:
    N := 10:
    a := proc (n) option remember; if n < 0 then 0 else A010816(n) + add( (-1)^(k+1)*a(n - (1/2)*k*(3*k-1) ), k = -N..-1) + add( (-1)^(k+1)*a(n - (1/2)*k*(3*k-1) ), k = 1..N) end if; end proc:
    seq(a(n), n = 0..100); # Peter Bala, Apr 06 2022
  • Mathematica
    terms = 78; Clear[s]; s[n_] := s[n] = Product[(1 - x^k)^2, {k, 1, n}] // Expand // CoefficientList[#, x]& // Take[#, terms]&; s[n = 10]; s[n = 2*n]; While[s[n] != s[n - 1], n = 2*n]; A002107 = s[n] (* Jean-François Alcover, Jan 17 2013 *)
    a[ n_] := SeriesCoefficient[ QPochhammer[ x]^2, {x, 0, n}]; (* Michael Somos, Jan 31 2015 *)
    a[ n_] := SeriesCoefficient[ Product[ 1 - x^k, {k, n}]^2, {x, 0, n}]; (* Michael Somos, Jan 31 2015 *)
  • PARI
    {a(n) = my(A, p, e, x); if( n<0, 0, n = 12*n + 1; A = factor(n); prod( k=1, matsize(A)[1], [p, e] = A[k,]; if( p<5, 0, p%12>1, if( e%2, 0, (-1)^((p%12==5) * e/2)), for( i=1, sqrtint(p\9), if( issquare(p - 9*i^2), x=i; break)); (e + 1) * (-1)^(e*x))))}; /* Michael Somos, Aug 30 2006 */
    
  • PARI
    {a(n) = if( n<0, 0, polcoeff( eta(x + x * O(x^n))^2, n))}; /* Michael Somos, Aug 30 2006 */
    
  • PARI
    Vec(eta(x)^2) \\ Charles R Greathouse IV, Apr 22 2016
    

Formula

Expansion of q^(-1/12) * eta(q)^2 in powers of q. - Michael Somos, Mar 06 2012
Euler transform of period 1 sequence [ -2, ...]. - Michael Somos, Mar 06 2012
a(n) = b(12*n + 1) where b(n) is multiplicative and b(2^e) = b(3^e) = 0^e, b(p^e) = (1 + (-1)^e) / 2 if p == 7, 11 (mod 12), b(p^e) = (-1)^(e/2) * (1 + (-1)^e) / 2 if p == 5 (mod 12), b(p^e) = (e + 1) * (-1)^(e*x) if p == 1 (mod 12) where p = x^2 + 9*y^2. - Michael Somos, Sep 16 2006
Convolution inverse of A000712.
a(0) = 1, a(n) = -(2/n)*Sum{k = 0..n-1} a(k)*sigma_1(n-k). - Joerg Arndt, Feb 05 2011
Expansion of f(-x)^2 in powers of x where f() is a Ramanujan theta function. - Michael Somos, May 17 2015
G.f. is a period 1 Fourier series which satisfies f(-1 / (144 t)) = 12 (t/i) f(t) where q = exp(2 Pi i t). - Michael Somos, May 17 2015
a(n) = Sum_{k=0..n} A010815(k)*A010815(n-k); self convolution of A010815. - Gevorg Hmayakyan, Sep 18 2016
G.f.: Sum_{m, n in Z, n >= 2*|m|} (-1)^n * x^((3*(2*n + 1)^2 - (6*m + 1)^2)/24). - Seiichi Manyama, Oct 01 2016
G.f.: exp(-2*Sum_{k>=1} x^k/(k*(1 - x^k))). - Ilya Gutkovskiy, Feb 05 2018
From Peter Bala, Jan 02 2021: (Start)
For prime p congruent to 5, 7 or 11 (mod 12), a(n*p^2 + (p^2 - 1)/12) = e*a(n), where e = 1 if p == 7 or 11 (mod 12) and e = -1 if p == 5 (mod 12).
If n and p are coprime then a(n*p + (p^2 - 1)/12) = 0. See Cooper et al., Theorem 1. (End)
With the convention that a(n) = 0 for n < 0 we have the recurrence a(n) = A010816(n) + Sum_{k a nonzero integer} (-1)^(k+1)*a(n - k*(3*k-1)/2), where A010816(n) = (-1)^m*(2*m+1) if n = m*(m + 1)/2, with m positive, is a triangular number else equals 0. For example, n = 10 = (4*5)/2 is a triangular number, A010816(10) = 9, and so a(10) = 9 + a(9) + a(8) - a(5) - a(3) = 9 - 2 - 2 - 2 - 2 = 1. - Peter Bala, Apr 06 2022

A258232 Decimal expansion of Integral_{x=0..1} Product_{k>=1} (1-x^k) dx.

Original entry on oeis.org

3, 6, 8, 4, 1, 2, 5, 3, 5, 9, 3, 1, 4, 3, 3, 6, 5, 2, 3, 2, 1, 3, 1, 6, 5, 9, 7, 3, 2, 7, 8, 5, 1, 0, 1, 5, 0, 1, 4, 2, 4, 1, 3, 0, 3, 9, 2, 8, 8, 1, 9, 9, 6, 8, 3, 0, 3, 6, 1, 5, 8, 0, 6, 6, 8, 2, 8, 1, 4, 7, 3, 0, 0, 8, 8, 9, 0, 3, 4, 3, 9, 2, 9, 8, 9, 0, 6, 3, 4, 4, 2, 4, 2, 4, 1, 4, 9, 9, 2, 1, 7, 6, 7, 1, 2, 8
Offset: 0

Views

Author

Vaclav Kotesovec, May 24 2015

Keywords

Examples

			0.3684125359314336523213165973278510150142413039288199683036158...
		

References

  • József Sándor and Borislav Crstici, Handbook of Number theory II, Kluwer Academic Publishers, 2004, Chapter 4, p. 424.

Crossrefs

Cf. A258406 (m=2), A258407 (m=3), A258404 (m=4), A258405 (m=5).

Programs

  • Maple
    evalf(8*sqrt(3/23)*Pi*sinh(sqrt(23)*Pi/6)/(2*cosh(sqrt(23)*Pi/3)-1), 123);
    evalf(Sum((-1)^n/((3*n-1)*n/2 + 1), n=-infinity..infinity), 123);
  • Mathematica
    RealDigits[N[8*Sqrt[3/23]*Pi*Sinh[Sqrt[23]*Pi/6] / (2*Cosh[Sqrt[23]*Pi/3]-1),120]][[1]]
  • PARI
    8*Pi*sqrt(3/23) * sinh(sqrt(23)*Pi/6) / (2*cosh(sqrt(23)*Pi/3) - 1) \\ Michel Marcus, Nov 28 2018

Formula

Equals 8*Pi*sqrt(3/23) * sinh(sqrt(23)*Pi/6) / (2*cosh(sqrt(23)*Pi/3) - 1).
From Amiram Eldar, Feb 04 2024: (Start)
Equals 2 * Sum_{k=-oo..oo} (-1)^k/(3*k^2 + k + 2).
Equals Sum_{k>=0} (-1)^A000120(k)/(A029931(k)+1) (Borwein and Borwein, 1992). (End)

A258414 Decimal expansion of Integral_{x=0..1} Product_{k>=1} (1-x^(24*k)) dx.

Original entry on oeis.org

9, 4, 9, 7, 0, 3, 1, 2, 6, 2, 9, 4, 0, 0, 9, 3, 9, 5, 2, 6, 3, 4, 9, 8, 4, 9, 1, 7, 4, 5, 7, 4, 1, 5, 1, 5, 8, 7, 3, 6, 5, 1, 9, 5, 0, 9, 0, 9, 6, 9, 2, 9, 4, 4, 8, 8, 0, 9, 1, 7, 6, 5, 4, 3, 6, 8, 3, 0, 5, 1, 9, 5, 5, 6, 8, 7, 9, 2, 8, 8, 1, 7, 2, 6, 0, 0, 6, 8, 0, 3, 2, 8, 4, 8, 3, 5, 3, 5, 0, 1, 6, 8, 7, 2, 9, 0
Offset: 0

Views

Author

Vaclav Kotesovec, May 29 2015

Keywords

Comments

Integral_{x=-1..1} Product_{k>=1} (1-x^(24*k)) dx = Pi^2/(3*sqrt(3)) = 1.89940625258801878... . - Vaclav Kotesovec, Jun 02 2015
Equals the value of the Dirichlet L-series of a non-principal character modulo 12 (A110161) at s=2. - Jianing Song, Nov 16 2019

Examples

			0.9497031262940093952634984917457415158736519509096929448809176543683...
		

Crossrefs

Programs

  • Maple
    evalf(Pi^2/(6*sqrt(3)), 120);
  • Mathematica
    RealDigits[Pi^2/(6*Sqrt[3]),10,120][[1]]
    N[Sum[(-1)^n/(12*n*(3n-1)+1),{n,-Infinity,Infinity}],105]

Formula

Equals Pi^2/(6*sqrt(3)).
Equals Sum_{k>=1} A110161(n)/k^2 = Sum_{k>=1} Kronecker(12,k)/k^2. - Jianing Song, Nov 16 2019
Equals -Integral_{x=0..oo} log(x)/(x^6 + 1) dx. - Amiram Eldar, Aug 12 2020
Equals 1 + Sum_{k>=1} ( (-1)^k/(6*k-1)^2 + (-1)^k/(6*k+1)^2 ). - Sean A. Irvine, Jul 18 2021
Equals 1/(Product_{p prime == 1 or 11 (mod 12)} (1 - 1/p^2) * Product_{p prime == 5 or 7 (mod 12)} (1 + 1/p^2)). - Amiram Eldar, Dec 17 2023

A258404 Decimal expansion of Integral_{x=0..1} Product_{k>=1} (1-x^k)^4 dx.

Original entry on oeis.org

1, 6, 1, 8, 2, 0, 2, 4, 2, 2, 9, 4, 8, 5, 6, 5, 6, 1, 8, 0, 2, 6, 1, 3, 3, 4, 9, 8, 5, 7, 8, 6, 5, 3, 4, 3, 1, 3, 0, 6, 8, 5, 7, 8, 2, 8, 8, 0, 1, 8, 9, 9, 0, 3, 9, 8, 0, 4, 2, 9, 4, 5, 3, 5, 7, 9, 5, 3, 4, 1, 5, 3, 8, 0, 4, 3, 7, 1, 4, 8, 9, 6, 8, 8, 5, 3, 3, 7, 1, 2, 9, 9, 2, 1, 5, 8, 5, 4, 4, 8, 5, 2, 1, 8, 9, 9
Offset: 0

Views

Author

Vaclav Kotesovec, May 29 2015

Keywords

Examples

			0.16182024229485656180261334985786534313068578288018990398...
		

Crossrefs

Programs

  • Maple
    evalf(Sum((2*Pi*(-1)^m / cosh(sqrt(7 - 4*m + 12*m^2)*Pi/2)), m=-infinity..infinity), 120); # Vaclav Kotesovec, Dec 04 2015
  • Mathematica
    nmax=200; p=1; q4=Table[PrintTemporary[n]; p=Expand[p*(1-x^n)^4]; Total[CoefficientList[p,x]/Range[1,Exponent[p,x]+1]],{n,1,nmax}]; q4n=N[q4,1000]; Table[SequenceLimit[Take[q4n,j]],{j,Length[q4n]-100,Length[q4n],10}]
    NSum[2*(-1)^m*Pi/Cosh[Sqrt[7 - 4*m + 12*m^2]*Pi/2], {m, -Infinity, Infinity}, WorkingPrecision -> 120, NSumTerms -> 100] (* Vaclav Kotesovec, Dec 04 2015 *)
    RealDigits[NIntegrate[QPochhammer[x]^4, {x, 0, 1}, WorkingPrecision -> 120], 10, 106][[1]] (* Vaclav Kotesovec, Oct 10 2023 *)
  • PARI
    default(realprecision, 93);
    b(n) = cosh(sqrt(7 - 4*n + 12*n^2)*Pi/2);
    2*Pi*(1/b(0) + sumalt(n=1, (-1)^n*(1/b(n) + 1/b(-n)))) \\ Gheorghe Coserea, Sep 26 2018

Formula

Sum_{m = -infinity..infinity} (2*Pi*(-1)^m / cosh(sqrt(7 - 4*m + 12*m^2)*Pi/2)). - Vaclav Kotesovec, Dec 04 2015

Extensions

More digits from Vaclav Kotesovec, Oct 10 2023

A258405 Decimal expansion of Integral_{x=0..1} Product_{k>=1} (1-x^k)^5 dx.

Original entry on oeis.org

1, 3, 7, 8, 0, 1, 0, 7, 0, 8, 4, 6, 5, 5, 4, 6, 4, 2, 8, 4, 5, 3, 8, 6, 1, 3, 1, 4, 0, 2, 1, 9, 3, 8, 4, 3, 0, 8, 4, 5, 2, 2, 5, 4, 1, 2, 3, 2, 6, 2, 5, 9, 8, 2, 6, 8, 3, 9, 3, 7, 0, 0, 3, 7, 0, 9, 2, 4, 8, 6, 3, 1, 0, 7, 7, 3, 1, 8, 1, 7, 0, 4, 8, 9, 3, 6, 2, 9, 1, 7, 6, 9, 8, 5, 9, 2, 4, 3, 4, 4, 1, 4
Offset: 0

Views

Author

Vaclav Kotesovec, May 29 2015

Keywords

Examples

			0.137801070846554642845386131402193843084522541232625982683937003709248631...
		

Crossrefs

Programs

  • Maple
    evalf(Sum(Sum(2*Pi*(-1)^(h+m) / cosh(sqrt(7 - 4*h + 12*h^2 - 4*m + 12*m^2)*Pi/2), m=-infinity..infinity), h=-infinity..infinity), 120); # Vaclav Kotesovec, Dec 04 2015
  • Mathematica
    nmax=200; p=1; q5=Table[PrintTemporary[n]; p=Expand[p*(1-x^n)^5]; Total[CoefficientList[p,x]/Range[1,Exponent[p,x]+1]],{n,1,nmax}]; q5n=N[q5,1000]; Table[SequenceLimit[Take[q5n,j]],{j,Length[q5n]-100,Length[q5n],10}]
    nterms = 40; N[Sum[Sum[2*Pi*(-1)^(h+m) / Cosh[Sqrt[7 - 4*h + 12*h^2 - 4*m + 12*m^2]*Pi/2], {m, -nterms, nterms}], {h, -nterms, nterms}], 100] (* Vaclav Kotesovec, Dec 04 2015 *)
    RealDigits[NIntegrate[QPochhammer[x]^5, {x, 0, 1}, WorkingPrecision -> 120], 10, 106][[1]] (* Vaclav Kotesovec, Oct 10 2023 *)

Formula

Sum_{m = -infinity..infinity} (Sum_{h = -infinity..infinity} (2*Pi*(-1)^(h+m) / cosh(sqrt(7 - 4*h + 12*h^2 - 4*m + 12*m^2)*Pi/2))). - Vaclav Kotesovec, Dec 04 2015

A258407 Decimal expansion of Integral_{x=0..1} Product_{k>=1} (1-x^k)^3 dx.

Original entry on oeis.org

1, 9, 6, 8, 8, 0, 6, 1, 5, 3, 1, 4, 5, 8, 8, 9, 7, 5, 3, 5, 3, 3, 5, 1, 3, 5, 8, 4, 7, 6, 9, 6, 6, 6, 8, 2, 9, 6, 6, 7, 3, 4, 3, 1, 7, 8, 3, 9, 1, 7, 5, 7, 5, 8, 6, 0, 9, 3, 3, 5, 7, 0, 6, 2, 6, 8, 9, 9, 0, 1, 5, 1, 1, 1, 1, 0, 5, 6, 2, 0, 9, 2, 2, 2, 9, 0, 5, 1, 0, 6, 0, 2, 7, 8, 3, 7, 4, 5, 6, 7, 3, 5, 4, 1, 8, 3
Offset: 0

Views

Author

Vaclav Kotesovec, May 29 2015

Keywords

Comments

In general, Integral_{x=0..1} Product_{k>=1} (1-x^(m*k))^3 dx = Sum_{n>=0} (-1)^n * (2*n+1) / (m*n*(n+1)/2 + 1) is equal to
if 0
if m = 8: Pi/4
if m > 8: 2*Pi / (m * cos((Pi/2)*sqrt(1-8/m)))
Special values: m=4: Pi/(2*cosh(Pi/2)), m=9: 4*Pi/(9*sqrt(3)).
---
Integral_{x=-1..1} Product_{k>=1} (1-x^k)^3 dx = 2*Pi*(1 + sqrt(2) * cosh(sqrt(7)*Pi/4)) / cosh(sqrt(7)*Pi/2) = 1.32639350417409769439126... . - Vaclav Kotesovec, Jun 02 2015

Examples

			0.1968806153145889753533513584769666829667343178391757586093357...
		

Crossrefs

Programs

  • Maple
    evalf(2*Pi/cosh(sqrt(7)*Pi/2), 120);
    evalf(Sum((-1)^n * (2*n+1) / (n*(n+1)/2 + 1), n=0..infinity), 120);
  • Mathematica
    RealDigits[2*Pi*Sech[(Sqrt[7]*Pi)/2],10,105][[1]]
  • PARI
    2*Pi/cosh((sqrt(7)*Pi)/2) \\ Stefano Spezia, Aug 23 2025

Formula

Equals 2*Pi/cosh(sqrt(7)*Pi/2).
Equals Sum_{n>=0} (-1)^n * (2*n+1) / (n*(n+1)/2 + 1).

A258408 Decimal expansion of Integral_{x=0..1} Product_{k>=1} (1-x^(2*k)) dx.

Original entry on oeis.org

5, 7, 7, 3, 3, 2, 1, 2, 0, 1, 8, 3, 9, 7, 9, 7, 0, 5, 5, 5, 2, 5, 4, 6, 9, 6, 2, 0, 1, 5, 9, 0, 4, 1, 5, 5, 0, 8, 0, 1, 1, 9, 3, 1, 3, 8, 3, 5, 6, 3, 4, 9, 2, 4, 5, 5, 8, 9, 0, 8, 8, 0, 3, 7, 5, 1, 5, 2, 5, 2, 1, 6, 4, 5, 1, 9, 8, 7, 7, 8, 1, 3, 5, 0, 6, 3, 7, 1, 0, 7, 0, 0, 0, 0, 0, 7, 1, 5, 4, 0, 9, 7, 8, 4, 7, 8
Offset: 0

Author

Vaclav Kotesovec, May 29 2015

Keywords

Comments

In general, Integral_{x=0..1} Product_{k>=1} (1-x^(m*k)) dx = Sum_{n} (-1)^n / (m*n*(3*n-1)/2 + 1) is equal to
if 0
(sqrt((24-m)*m) * (2*cosh(Pi/3*sqrt(24/m-1))-1))
if m = 24: Pi^2/(6*sqrt(3)) = A258414
if m > 24: 8*sqrt(3)*Pi*sin(Pi/6*sqrt(1-24/m)) /
(sqrt((m-24)*m) * (2*cos(Pi/3*sqrt(1-24/m))-1)).
Integral_{x=0..1} Product_{k=1..n} (1+x^(m*k)) dx, where m >= 1, is asymptotic to 2*(m+1)^(n+1)/(m*n^2).
Integral_{x=-1..1} Product_{k>=1} (1-x^(2*k)) dx = 8*Pi*sqrt(3/11) * sinh(sqrt(11)*Pi/6) / (2*cosh(sqrt(11)*Pi/3)-1) = 1.154664240367959678... . - Vaclav Kotesovec, Jun 02 2015

Examples

			0.5773321201839797055525469620159041550801193138356349245589088...
		

Crossrefs

Programs

  • Maple
    evalf(4*Pi*sqrt(3/11) * sinh(sqrt(11)*Pi/6) / (2*cosh(sqrt(11)*Pi/3) - 1), 120);
  • Mathematica
    RealDigits[4*Pi*Sqrt[3/11]*Sinh[Sqrt[11]*Pi/6] / (2*Cosh[Sqrt[11]*Pi/3] - 1),10,120][[1]]

Formula

Equals 4*Pi*sqrt(3/11) * sinh(sqrt(11)*Pi/6) / (2*cosh(sqrt(11)*Pi/3) - 1).
Showing 1-7 of 7 results.