E.g.f.: (1-3*exp(x)+exp(2*x))/(exp(x)-2).

Terms

a(0) =1a(1) =2a(2) =4a(3) =14a(4) =76a(5) =542a(6) =4684a(7) =47294a(8) =545836a(9) =7087262a(10) =102247564a(11) =1622632574a(12) =28091567596a(13) =526858348382