a(n) = (5/32)*4^n - floor((n^2 + 1)/2)*2^(n - 2).

Terms

a(0) =0a(1) =8a(2) =56a(3) =352a(4) =1760a(5) =8192a(6) =35712a(7) =151040a(8) =624128a(9) =2547712a(10) =10311680a(11) =41541632a(12) =166846464a(13) =668991488a(14) =2679603200a(15) =10726801408a(16) =42925948928a(17) =171746263040a(18) =687078899712