Generalized Fibonacci numbers.

Terms

a(0) =1a(1) =2a(2) =7a(3) =26a(4) =107a(5) =468a(6) =2141a(7) =10124a(8) =49101a(9) =242934a(10) =1221427a(11) =6222838a(12) =32056215a(13) =166690696a(14) =873798681a(15) =4612654808a(16) =24499322137a(17) =130830894666a(18) =702037771647