A268021 a(1) = a(2) = 1; if n > 2 then a(n) = a(n-1)*a(n-2) - a(n-2) - a(n-1).

1, 1, -1, -1, 3, -5, -13, 83, -1149, -94301, 108447299, -10226797095997, -1109068512255229713405, 11342218640394605506848882609549187, -12579297553175979435284002182896862386417808141640587517

Offset: 1

Author

José María Grau Ribas, Jan 24 2016

Keywords

• sign

Programs

Mathematica

a[1] = 1; a[2] = 1; a[n_] := a[n] = -a[n - 1] - a[n - 2] + a[n - 1]*a[n - 2];Table[a[n], {n, 20}]
nxt[{a_,b_}]:={b,a*b-a-b}; NestList[nxt,{1,1},20][[All,1]] (* Harvey P. Dale, Nov 29 2022 *)

Formula

|a(n)| ~ c^(phi^n), where phi = A001622 = (1+sqrt(5))/2 is the golden ratio and c = 1.097478514051533426... . - Vaclav Kotesovec, Jan 26 2016