a(0)=0, a(1)=1, a(2)=2, a(3)=3, a(4)=12; for n > 4, a(n) = 8*a(n-2) - a(n-4) - 3.

Terms

a(0) =0a(1) =1a(2) =2a(3) =3a(4) =12a(5) =20a(6) =91a(7) =154a(8) =713a(9) =1209a(10) =5610a(11) =9515a(12) =44164a(13) =74908a(14) =347699a(15) =589746a(16) =2737425a(17) =4643057a(18) =21551698a(19) =36554707a(20) =169676156a(21) =287794596a(22) =1335857547a(23) =2265802058a(24) =10517184217a(25) =17838621865a(26) =82801616186a(27) =140443172859a(28) =651895745268