a(n) = a(n-1)^2 + a(n-1), a(0)=1.A007018a(n) = a(n-1)^2 + a(n-1), a(0)=1.Terms a(0) =1a(1) =2a(2) =6a(3) =42a(4) =1806a(5) =3263442External referencesoeis: A007018