OFFSET
1,2
LINKS
FORMULA
G.f.: (B(x)-x)/(x(1-x)) where B(x) is g.f. of A002572.
EXAMPLE
G.f. = x + 2*x^2 + 4*x^3 + 7*x^4 + 12*x^5 + 21*x^6 + 37*x^7 + 65*x^8 + 115*x^9 + ...
MAPLE
v:= proc(c, d) option remember; if d<0 or c<0 then 0 elif d=c then 1 else add(v(i, d-c), i=1..2*c) fi end: a:= proc(n) option remember; if n=0 then 0 else a(n-1) +v(1, n) fi end: seq(a(n), n=1..40); # Alois P. Heinz, Aug 22 2008
MATHEMATICA
v[c_, d_] := v[c, d] = If[d<0 || c<0, 0, If[d == c, 1, Sum[v[i, d-c], {i, 1, 2c}]]]; a[n_] := a[n] = If[n == 0, 0, a[n-1]+v[1, n]]; Table[a[n], {n, 1, 29}] (* Jean-François Alcover, Mar 03 2014, after Alois P. Heinz *)
CROSSREFS
KEYWORD
nonn
AUTHOR
STATUS
approved