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.

A303970 Expansion of e.g.f. Product_{k>=1} 1/(1 - x^k)^H(k), where H(k) is the k-th harmonic number.

Original entry on oeis.org

1, 1, 5, 26, 199, 1599, 17053, 186276, 2460057, 34226729, 537669401, 8925732958, 163894885735, 3151342927823, 65678713377873, 1437541042260704, 33545591623360881, 819213454875992337, 21170268780829522093, 570252657062810041954, 16139888268919495959911, 475126022355752304699455, 14608848314409377281498213
Offset: 0

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Author

Ilya Gutkovskiy, May 03 2018

Keywords

Comments

a(n)/n! is the Euler transform of [1, 1 + 1/2, 1 + 1/2 + 1/3, 1 + 1/2 + 1/3 + 1/4, ...].

Crossrefs

Programs

  • Maple
    H:= proc(n) option remember; `if`(n=0, 0, 1/n+H(n-1)) end:
    b:= proc(n) option remember; `if`(n=0, 1, add(add(d*
          H(d), d=numtheory[divisors](j))*b(n-j), j=1..n)/n)
        end:
    a:= n-> n!*b(n):
    seq(a(n), n=0..20);  # Alois P. Heinz, May 03 2018
  • Mathematica
    nmax = 22; CoefficientList[Series[Product[1/(1 - x^k)^HarmonicNumber[k], {k, 1, nmax}], {x, 0, nmax}], x] Range[0, nmax]!
    a[n_] := a[n] = If[n == 0, 1, Sum[Sum[d HarmonicNumber[d], {d, Divisors[k]}] a[n - k], {k, 1, n}]/n]; Table[n! a[n], {n, 0, 22}]

Formula

E.g.f.: Product_{k>=1} 1/(1 - x^k)^(A001008(k)/A002805(k)).