A203901 a(n)=f(a(n-1)+1,a(n-2)+1,a(n-3)), where f(x,y,z)=yz+zx+xy and (a(1),a(2),a(3))=(0,0,1).

0, 0, 1, 2, 6, 31, 302, 11706, 3919531, 47073195302, 185055980038616706, 8711901623180875318209094531, 1612189902974799120179526719227635256224945302

Offset: 1

Author

Clark Kimberling, Jan 07 2012

Keywords

• nonn

Comments

For a guide to related sequences, see A203761.

Crossrefs

Cf. A203761.

Programs

Mathematica

a[1] = 0; a[2] = 0; a[3] = 1;
a[n_] := SymmetricPolynomial[2, {1 + a[n - 1], 1 + a[n - 2], a[n - 3]}]
Table[a[n], {n, 1, 16}] (* A203901 *)
nxt[{a_,b_,c_}]:={b,c,Total[Times@@@Subsets[{a,b+1,c+1},{2}]]}; NestList[nxt,{0,0,1},15][[All,1]] (* Harvey P. Dale, Nov 01 2022 *)