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 1-2 of 2 results.

A328054 Expansion of e.g.f. log(1 + x / (1 - x)^2).

Original entry on oeis.org

0, 1, 3, 8, 18, 24, 0, 720, 15120, 161280, 1088640, 3628800, 0, 479001600, 18681062400, 348713164800, 3923023104000, 20922789888000, 0, 6402373705728000, 364935301226496000, 9731608032706560000, 153272826515128320000, 1124000727777607680000, 0, 620448401733239439360000
Offset: 0

Views

Author

Ilya Gutkovskiy, Oct 03 2019

Keywords

Comments

Logarithmic transform of A001563.

Crossrefs

Cf. A001563, A008588 (positions of 0's), A009306, A082579, A328055.

Programs

  • Maple
    b:= proc(n) option remember; n*n! end:
    a:= proc(n) option remember; `if`(n=0, 0, b(n)-
          add(binomial(n, j)*j*b(n-j)*a(j), j=1..n-1)/n)
        end:
    seq(a(n), n=0..25);  # Alois P. Heinz, Oct 04 2019
  • Mathematica
    nmax = 25; CoefficientList[Series[Log[1 + x/(1 - x)^2], {x, 0, nmax}], x] Range[0, nmax]!
    Join[{0}, Table[2 (n - 1)! (1 - Cos[Pi n/3]), {n, 1, 25}]]
  • PARI
    my(x='x+O('x^30)); concat(0, Vec(serlaplace(log(1 + x / (1 - x)^2)))) \\ Michel Marcus, Oct 04 2019

Formula

E.g.f.: log(1 + Sum_{k>=1} k * x^k).
D-finite with recurrence a(n+3) = n*(n+1)*(n+2)*a(n) - 2*(n+2)*(n+1)*a(n+1) + 2*(n+2)*a(n+2). - Robert Israel, Jan 16 2023

A366953 Expansion of e.g.f. -log(1 - x^2/(1-x)^3).

Original entry on oeis.org

0, 0, 2, 18, 156, 1560, 18600, 262080, 4284000, 79833600, 1671788160, 38878963200, 994367404800, 27741377664000, 838406080512000, 27287153858764800, 951529253875200000, 35392677532692480000, 1398727294865252352000, 58529661706809925632000, 2585234639710708457472000
Offset: 0

Views

Author

Enrique Navarrete, Oct 29 2023

Keywords

Comments

a(n) is the number of ways to choose two elements from each branch of labeled octopuses with n nodes.
A328055(n) is the corresponding sequence if we choose one element only.

Crossrefs

Showing 1-2 of 2 results.