a(n) = (3*2^(n+1) - 8 - (-2)^n)/6.

Terms

a(0) =1a(1) =2a(2) =8a(3) =12a(4) =36a(5) =52a(6) =148a(7) =212a(8) =596a(9) =852a(10) =2388a(11) =3412a(12) =9556a(13) =13652a(14) =38228a(15) =54612a(16) =152916a(17) =218452a(18) =611668a(19) =873812a(20) =2446676a(21) =3495252a(22) =9786708a(23) =13981012a(24) =39146836a(25) =55924052a(26) =156587348a(27) =223696212a(28) =626349396a(29) =894784852