A306028 Number of length-n restricted growth strings (RGS) with growth <= four and first element in [4].

1, 4, 26, 214, 2096, 23578, 297692, 4150798, 63148652, 1038505282, 18324165284, 344791676446, 6883214479964, 145160792680210, 3221934217192772, 75022325591768782, 1827426669105650588, 46448931646662304066, 1229212096172351894852, 33800410177112965182910

Offset: 0

Author

Alois P. Heinz, Jun 17 2018

Keywords

• nonn

Links

• Alois P. Heinz, Table of n, a(n) for n = 0..459

Crossrefs

Column k=4 of A306024.

Cf. A305964.

Programs

Maple

b:= proc(n, m) option remember; `if`(n=0, 1,
      add(b(n-1, max(m, j)), j=1..m+4))
    end:
a:= n-> b(n, 0):
seq(a(n), n=0..25);
# second Maple program:
a:= n-> n!*coeff(series(exp(add((exp(j*x)-1)/j, j=1..4)), x, n+1), x, n):
seq(a(n), n=0..25);

Formula

E.g.f.: exp(Sum_{j=1..4} (exp(j*x)-1)/j).