a(n) = 4^(floor(n/2))+4^(floor(n/2)-1)-4^(floor((n-1)/3)).

Terms

a(0) =4a(1) =4a(2) =16a(3) =16a(4) =76a(5) =64a(6) =304a(7) =304a(8) =1216a(9) =1216a(10) =5056a(11) =4864a(12) =20224a(13) =20224a(14) =80896a(15) =80896a(16) =326656a(17) =323584a(18) =1306624a(19) =1306624a(20) =5226496a(21) =5226496a(22) =20955136a(23) =20905984a(24) =83820544a(25) =83820544a(26) =335282176a(27) =335282176a(28) =1341915136a(29) =1341128704