a(n) = if n even then P((n-2)/2)+P(n/2) otherwise 3*P((n+1)/2)+P((n-1)/2) where P(i) are the Pell numbers (A000129).

A189050

a(n) = if n even then P((n-2)/2)+P(n/2) otherwise 3*P((n+1)/2)+P((n-1)/2) where P(i) are the Pell numbers (A000129).

Terms

    a(0) =3a(1) =1a(2) =7a(3) =3a(4) =17a(5) =7a(6) =41a(7) =17a(8) =99a(9) =41a(10) =239a(11) =99a(12) =577a(13) =239a(14) =1393a(15) =577a(16) =3363a(17) =1393a(18) =8119a(19) =3363a(20) =19601a(21) =8119a(22) =47321a(23) =19601a(24) =114243a(25) =47321a(26) =275807a(27) =114243a(28) =665857a(29) =275807

External references