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 1-3 of 3 results.

A058864 Number of labeled chordal graphs (connected or not) on n nodes with no induced path P_4.

Original entry on oeis.org

1, 2, 8, 49, 402, 4144, 51515, 750348, 12537204, 236424087, 4967735896, 115102258660, 2915655255385, 80164472149454, 2377679022913612, 75674858155603353, 2572626389524849478, 93040490884813025684, 3566833833735159397963, 144485408698878208399296
Offset: 1

Views

Author

Robert Castelo, Jan 06 2001

Keywords

Comments

A subclass of chordal-comparability graphs.

References

  • Miklos Bona, editor, Handbook of Enumerative Combinatorics, CRC Press, 2015, p. 417.

Links

Crossrefs

Cf. A007134, A058863, A058865.
Cf. variants: A196555, A196556, A196557.

Programs

  • Mathematica
    Rest[With[{nmax = 50}, CoefficientList[Series[Exp[-LambertW[Exp[-x] - 1]], {x, 0, nmax}], x]*Range[0, nmax]!]] (* G. C. Greubel, Nov 14 2017 *)
a[n_] := Sum[(-1)^(n-k)*StirlingS2[n, k]*(k+1)^(k-1), {k, 0, n}];
Array[a, 18] (* Jean-François Alcover, Dec 17 2017, after Vladeta Jovovic *)
  • PARI
    {a(n)=polcoeff(sum(m=1, n, (m+1)^(m-1)*x^m/prod(k=1, m, 1+k*x+x*O(x^n))), n)} /* Paul D. Hanna, Jul 20 2011 */
  • PARI
    for(n=1,10, print1(sum(k=0, n, (-1)^(n-k)*stirling(n,k,2)*(k+1)^(k-1)), ", ")) \\ G. C. Greubel, Nov 14 2017

Formula

A058863 and A058864 satisfy:
1) c(n) = 1 + Sum_{k=1..n-2} binomial(n, k)*(t(n-k) - c(n-k))
2) t(n) = c(n) + Sum_{k=1..n-1} k*c(k)*binomial(n, k)*t(n-k)/n
where c(n) (A058863) is the number of connected graphs of this type and t(n) (A058864) is the total number of such graphs.
O.g.f.: Sum_{n>=1} (n+1)^(n-1) * x^n / Product_{k=1..n} (1+k*x). - Paul D. Hanna, Jul 20 2011
E.g.f.: exp(-LambertW(exp(-x)-1)). - Vladeta Jovovic, Nov 22 2002
a(n) = Sum_{k=0..n} (-1)^(n-k)*Stirling2(n, k)*(k+1)^(k-1). - Vladeta Jovovic, Nov 12 2003
a(n) ~ sqrt(exp(1)-1) * exp(1-n) * n^(n-1) * (1-log(exp(1)-1))^(1/2-n). - Vaclav Kotesovec, Oct 18 2013

Extensions

Formulae edited and completed by Michel Marcus, Apr 07 2013

A196555 O.g.f.: Sum_{n>=0} 2*(n+2)^(n-1) * x^n / Product_{k=1..n} (1+k*x).

Original entry on oeis.org

1, 2, 6, 28, 186, 1614, 17332, 222254, 3317326, 56532264, 1083571422, 23081180918, 541047188936, 13843339479298, 383952455939662, 11475711580482268, 367729128426998450, 12577206203908139494, 457341567152354085700, 17619050162270848917366
Offset: 0

Views

Author

Paul D. Hanna, Oct 03 2011

Keywords

Examples

			O.g.f.: A(x) = 1 + 2*x + 6*x^2 + 28*x^3 + 186*x^4 + 1614*x^5 +...
where the o.g.f. is given by:
A(x) = 1 + 2*3^0*x/(1+x) + 2*4^1*x^2/((1+x)*(1+2*x)) + 2*5^2*x^3/((1+x)*(1+2*x)*(1+3*x)) + 2*6^3*x^4/((1+x)*(1+2*x)*(1+3*x)*(1+4*x)) +...
E.g.f.: A(x) = 1 + 2*x + 6*x^2/2! + 28*x^3/3! + 186*x^4/4! + 1614*x^5/5! +...
where the e.g.f. is given by:
A(x)^(1/2) = 1 + x + 2*x^2/2! + 8*x^3/3! + 49*x^4/4! + 402*x^5/5! + 4144*x^6/6! +...+ A058864(n)*x^n/n! +...

Links

Crossrefs

Cf. A058864, A196556, A196557.

Programs

  • Mathematica
    CoefficientList[Series[E^(-2*LambertW[E^(-x)-1]), {x, 0, 20}], x]* Range[0, 20]! (* Vaclav Kotesovec, Jul 09 2013 *)
  • PARI
    {a(n)=polcoeff(sum(m=0, n, 2*(m+2)^(m-1)*x^m/prod(k=1, m, 1+k*x+x*O(x^n))), n)}
  • PARI
    {A058864(n)=polcoeff(sum(m=0, n, (m+1)^(m-1)*x^m/prod(k=1, m, 1+k*x+x*O(x^n))), n)}
{a(n) = sum(k=0,n,binomial(n,k)*A058864(n-k)*A058864(k))}
  • PARI
    a(n)=sum(k=0, n, (-1)^(n-k)*stirling(n, k, 2)*2*(k+2)^(k-1));
  • PARI
    my(N=20, x='x+O('x^N)); Vec(serlaplace(exp(-2*lambertw(exp(-x)-1)))) \\ Seiichi Manyama, Nov 21 2021

Formula

E.g.f.: exp(-2*LambertW(exp(-x)-1)).
a(n) = Sum_{k=0..n} (-1)^(n-k)*Stirling2(n, k)*2*(k+2)^(k-1).
a(n) = Sum_{k=0..n} C(n,k)*A058864(n-k)*A058864(k); exponential convolution of A058864, which is the number of labeled chordal graphs (connected or not) on n nodes with no induced path P_4.
a(n) ~ 2*sqrt(exp(1)-1) * n^(n-1) / (exp(n-2) * (1-log(exp(1)-1))^(n-1/2)). - Vaclav Kotesovec, Jul 09 2013

A196556 O.g.f.: Sum_{n>=0} 3*(n+3)^(n-1) * x^n / Product_{k=1..n} (1+k*x).

Original entry on oeis.org

1, 3, 12, 66, 483, 4476, 50454, 671649, 10328118, 180341094, 3527385345, 76435691250, 1818255212490, 47118807865863, 1321527658352016, 39889359465259446, 1289471521115731611, 44450463108654209136, 1627806562174453037802
Offset: 0

Views

Author

Paul D. Hanna, Oct 03 2011

Keywords

Examples

			O.g.f.: A(x) = 1 + 3*x + 12*x^2 + 66*x^3 + 483*x^4 + 4476*x^5 +...
where the o.g.f. is given by:
A(x) = 1 + 3*4^0*x/(1+x) + 3*5^1*x^2/((1+x)*(1+2*x)) + 3*6^2*x^3/((1+x)*(1+2*x)*(1+3*x)) + 3*7^3*x^4/((1+x)*(1+2*x)*(1+3*x)*(1+4*x)) +...
E.g.f.: A(x) = 1 + 3*x + 12*x^2/2! + 66*x^3/3! + 483*x^4/4! + 4476*x^5/5! +...
where the e.g.f. is given by:
A(x)^(1/3) = 1 + x + 2*x^2/2! + 8*x^3/3! + 49*x^4/4! + 402*x^5/5! + 4144*x^6/6! +...+ A058864(n)*x^n/n! +...

Links

Crossrefs

Cf. A058864, A196555, A196557.

Programs

  • Mathematica
    CoefficientList[Series[E^(-3*LambertW[E^(-x)-1]), {x, 0, 20}], x]* Range[0, 20]! (* Vaclav Kotesovec, Jul 09 2013 *)
  • PARI
    {a(n)=polcoeff(sum(m=0, n, 3*(m+3)^(m-1)*x^m/prod(k=1, m, 1+k*x+x*O(x^n))), n)}
  • PARI
    /* E.g.f. = G(x)^3 where G(x) = e.g.f. of A058864 */
{A058864(n)=polcoeff(sum(m=0, n, (m+1)^(m-1)*x^m/prod(k=1, m, 1+k*x+x*O(x^n))), n)}
{a(n)=n!*polcoeff(sum(k=0,n,A058864(k)*x^k/k!+x*O(x^n))^3,n)}
  • PARI
    a(n)=sum(k=0, n, (-1)^(n-k)*stirling(n, k, 2)*3*(k+3)^(k-1));
  • PARI
    my(N=20, x='x+O('x^N)); Vec(serlaplace(exp(-3*lambertw(exp(-x)-1)))) \\ Seiichi Manyama, Nov 21 2021

Formula

E.g.f.: exp(-3*LambertW(exp(-x)-1)).
a(n) = Sum_{k=0..n} (-1)^(n-k)*Stirling2(n, k)*3*(k+3)^(k-1).
E.g.f.: A(x) = G(x)^3 where G(x) = e.g.f. of A058864, which is the number of labeled chordal graphs (connected or not) on n nodes with no induced path P_4.
a(n) ~ 3*sqrt(exp(1)-1) * n^(n-1) / (exp(n-3) * (1-log(exp(1)-1))^(n-1/2)). - Vaclav Kotesovec, Jul 09 2013
Showing 1-3 of 3 results.

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