a(n) = 5^n - 2^(n - 1) for n > 0; a(0) = 1.

Terms

a(0) =1a(1) =4a(2) =23a(3) =121a(4) =617a(5) =3109a(6) =15593a(7) =78061a(8) =390497a(9) =1952869a(10) =9765113a(11) =48827101a(12) =244138577a(13) =1220699029a(14) =6103507433a(15) =30517561741a(16) =152587857857a(17) =762939387589