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.

A370985 Expansion of e.g.f. (1/x) * Series_Reversion( x*(1 - x^3*exp(x)) ).

Original entry on oeis.org

1, 0, 0, 6, 24, 60, 3000, 45570, 403536, 10644984, 297562320, 5517833310, 142801022760, 5076208052916, 150282366476424, 4713707747551530, 189345734667052320, 7517503455423740400, 295622259241028433696, 13370535071068474177974, 642403497550155241197240
Offset: 0

Views

Author

Seiichi Manyama, Mar 06 2024

Keywords

Crossrefs

Programs

  • PARI
    my(N=30, x='x+O('x^N)); Vec(serlaplace(serreverse(x*(1-x^3*exp(x)))/x))
    
  • PARI
    a(n) = sum(k=0, n\3, k^(n-3*k)*(n+k)!/(k!*(n-3*k)!))/(n+1);

Formula

a(n) = (1/(n+1)) * Sum_{k=0..floor(n/3)} k^(n-3*k) * (n+k)!/(k! * (n-3*k)!).

A371042 E.g.f. satisfies A(x) = 1 + x^2*exp(x*A(x)).

Original entry on oeis.org

1, 0, 2, 6, 12, 140, 1470, 10122, 114296, 1874952, 25462170, 379431470, 7546461252, 151797222876, 3066316693622, 72101615826450, 1843378516587120, 47860832586054032, 1338908395558366386, 40675047500003794902, 1282380661224172506620
Offset: 0

Views

Author

Seiichi Manyama, Mar 09 2024

Keywords

Crossrefs

Programs

  • Mathematica
    nmax = 20; CoefficientList[Series[1 - LambertW[-E^x*x^3]/x, {x, 0, nmax}], x] * Range[0, nmax]! (* Vaclav Kotesovec, Mar 10 2024 *)
  • PARI
    a(n) = n!*sum(k=0, n\2, k^(n-2*k)*binomial(n-2*k+1, k)/((n-2*k+1)*(n-2*k)!));

Formula

a(n) = n! * Sum_{k=0..floor(n/2)} k^(n-2*k) * binomial(n-2*k+1,k)/( (n-2*k+1)*(n-2*k)! ).
From Vaclav Kotesovec, Mar 10 2024: (Start)
E.g.f.: 1 - LambertW(-exp(x)*x^3)/x.
a(n) ~ sqrt(1 + LambertW(exp(-1/3)/3)) * n^(n-1) / (exp(n) * 3^(n + 1/2) * LambertW(exp(-1/3)/3)^(n+1)). (End)

A371043 E.g.f. satisfies A(x) = 1 + x^2*A(x)*exp(x*A(x)).

Original entry on oeis.org

1, 0, 2, 6, 36, 380, 3630, 47082, 725816, 12132360, 235801530, 5083309550, 119757623172, 3103443520476, 87082536196838, 2632399338834930, 85471932351187440, 2961803643600574352, 109154615479427298546, 4264407640037365789014, 175984871341042826680700
Offset: 0

Views

Author

Seiichi Manyama, Mar 09 2024

Keywords

Crossrefs

Programs

  • PARI
    a(n) = n!*sum(k=0, n\2, k^(n-2*k)*binomial(n-k+1, k)/((n-k+1)*(n-2*k)!));

Formula

a(n) = n! * Sum_{k=0..floor(n/2)} k^(n-2*k) * binomial(n-k+1,k)/( (n-k+1)*(n-2*k)! ).
Showing 1-3 of 3 results.