a(n) = A027082(n, 2n-7).

Terms

a(0) =1a(1) =3a(2) =9a(3) =31a(4) =105a(5) =352a(6) =1168a(7) =3828a(8) =12396a(9) =39698a(10) =125878a(11) =395686a(12) =1234426a(13) =3825911a(14) =11790893a(15) =36160491a(16) =110429221a(17) =336001043a(18) =1019092233a(19) =3082348295a(20) =9300339633a(21) =28002492673a(22) =84156758459a(23) =252507279805a(24) =756547966323