OFFSET
1,2
REFERENCES
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
P. R. Stein, personal communication.
LINKS
Alois P. Heinz, Table of n, a(n) for n = 1..100
P. R. Stein & N. J. A. Sloane, Correspondence, 1975
MAPLE
b:= proc(u, o, t) option remember; `if`(u+o=0, 1, add(`if`(t=3,
b(o-j, u+j-1, 1), b(u+j-1, o-j, t+1)), j=1..o))
end:
a:= n-> b(0, 3*n+1, 0):
seq(a(n), n=1..20); # Alois P. Heinz, Oct 06 2013
MATHEMATICA
b[u_, o_, t_] := b[u, o, t] = If[u+o == 0, 1, Sum[If[t == 3, b[o-j, u+j-1, 1], b[u+j-1, o-j, t+1]], {j, 1, o}]] ; a[n_] := b[0, 3*n+1, 0]; Table[a[n], {n, 1, 20}] (* Jean-François Alcover, Nov 25 2014, after Alois P. Heinz *)
CROSSREFS
KEYWORD
nonn
AUTHOR
EXTENSIONS
Typo in name fixed by Alois P. Heinz, Oct 06 2013
STATUS
approved