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 1-5 of 5 results.

A354551 Expansion of e.g.f. exp( x * exp(x^3/6) ).

Original entry on oeis.org

1, 1, 1, 1, 5, 21, 61, 211, 1401, 8065, 37241, 240021, 1997821, 13856701, 94418325, 874328911, 8304303281, 69158458881, 658339599601, 7454839614985, 78224066633781, 805961931388741, 9828080719704941, 124199805022959051, 1466207770078872745
Offset: 0

Views

Author

Seiichi Manyama, Aug 18 2022

Keywords

Comments

This sequence is different from A143567.

Crossrefs

Programs

  • Mathematica
    With[{nn=30},CoefficientList[Series[Exp[x*Exp[x^3/6]],{x,0,nn}],x] Range[0,nn]!] (* Harvey P. Dale, Mar 03 2025 *)
  • PARI
    my(N=30, x='x+O('x^N)); Vec(serlaplace(exp(x*(exp(x^3/6)))))
    
  • PARI
    a(n) = n!*sum(k=0, n\3, (n-3*k)^k/(6^k*k!*(n-3*k)!));

Formula

a(n) = n! * Sum_{k=0..floor(n/3)} (n - 3*k)^k/(6^k * k! * (n - 3*k)!).

A354552 Expansion of e.g.f. exp( x * exp(x^4/24) ).

Original entry on oeis.org

1, 1, 1, 1, 1, 6, 31, 106, 281, 946, 7561, 54286, 281161, 1207636, 7997991, 81996916, 701522641, 4580581916, 29742355441, 306369616636, 3632198902321, 34710574441096, 276645112305871, 2652825718776696, 35647605796451881, 458142859493786776
Offset: 0

Views

Author

Seiichi Manyama, Aug 18 2022

Keywords

Comments

This sequence is different from A143568.

Crossrefs

Programs

  • PARI
    my(N=30, x='x+O('x^N)); Vec(serlaplace(exp(x*(exp(x^4/24)))))
    
  • PARI
    a(n) = n!*sum(k=0, n\4, (n-4*k)^k/(24^k*k!*(n-4*k)!));

Formula

a(n) = n! * Sum_{k=0..floor(n/4)} (n - 4*k)^k/(24^k * k! * (n - 4*k)!).

A356029 a(n) = n! * Sum_{k=0..floor(n/2)} (n - 2*k)^k/(2^k * (n - 2*k)!).

Original entry on oeis.org

1, 1, 1, 4, 13, 61, 421, 2626, 27049, 245953, 3069721, 40222216, 576988501, 10058716669, 169773404893, 3596206855606, 73450508303761, 1775382487932001, 43993288886533489, 1183551336464017708, 34806599282992709341, 1043452963148195577181
Offset: 0

Views

Author

Seiichi Manyama, Aug 18 2022

Keywords

Crossrefs

Programs

  • Mathematica
    a[n_] := n! * Sum[(n - 2*k)^k/(2^k*(n - 2*k)!), {k, 0, Floor[n/2]}]; a[0] = 1; Array[a, 22, 0] (* Amiram Eldar, Aug 19 2022 *)
  • PARI
    a(n) = n!*sum(k=0, n\2, (n-2*k)^k/(2^k*(n-2*k)!));
    
  • PARI
    my(N=30, x='x+O('x^N)); Vec(serlaplace(sum(k=0, N, x^k/(k!*(1-k*x^2/2)))))

Formula

E.g.f.: Sum_{k>=0} x^k / (k! * (1 - k*x^2/2)).

A358264 Expansion of e.g.f. 1/(1 - x * exp(x^2/2)).

Original entry on oeis.org

1, 1, 2, 9, 48, 315, 2520, 23415, 248640, 2972025, 39463200, 576413145, 9184855680, 158550787395, 2947473809280, 58707685211175, 1247293022976000, 28156003910859825, 672972205556851200, 16978695795089253225, 450907982644863744000, 12573634144960773960075
Offset: 0

Views

Author

Seiichi Manyama, Nov 06 2022

Keywords

Crossrefs

Programs

  • PARI
    my(N=30, x='x+O('x^N)); Vec(serlaplace(1/(1-x*exp(x^2/2))))
    
  • PARI
    a(n) = n!*sum(k=0, n\2, (n-2*k)^k/(2^k*k!));

Formula

a(n) = n! * Sum_{k=0..floor(n/2)} (n - 2*k)^k/(2^k * k!).
a(n) ~ n! / ((1 + LambertW(1)) * LambertW(1)^(n/2)). - Vaclav Kotesovec, Nov 13 2022

A362660 E.g.f. satisfies A(x) = exp( x * exp(x^2/2) * A(x) ).

Original entry on oeis.org

1, 1, 3, 19, 161, 1791, 24847, 413449, 8036625, 178852753, 4486426091, 125279093259, 3854964555697, 129618443364463, 4728625129171959, 186034319795094481, 7851808690935373793, 353903271319498588641, 16966669198377512202643
Offset: 0

Views

Author

Seiichi Manyama, Apr 29 2023

Keywords

Crossrefs

Programs

  • PARI
    my(N=20, x='x+O('x^N)); Vec(serlaplace(exp(-lambertw(-x*exp(x^2/2)))))

Formula

E.g.f.: exp( -LambertW(-x * exp(x^2/2)) ).
a(n) = n! * Sum_{k=0..floor(n/2)} (n-2*k)^k * (n-2*k+1)^(n-2*k-1) / (2^k * k! * (n-2*k)!).
a(n) ~ sqrt(1 + LambertW(exp(-2))) * n^(n-1) / (exp(n-1) * LambertW(exp(-2))^(n/2)). - Vaclav Kotesovec, Aug 05 2025
Showing 1-5 of 5 results.