a(n) = 2^(n-1)*(6*n-10)+6.

Terms

a(0) =1a(1) =2a(2) =10a(3) =38a(4) =118a(5) =326a(6) =838a(7) =2054a(8) =4870a(9) =11270a(10) =25606a(11) =57350a(12) =126982a(13) =278534a(14) =606214a(15) =1310726a(16) =2818054a(17) =6029318a(18) =12845062a(19) =27262982a(20) =57671686a(21) =121634822a(22) =255852550a(23) =536870918a(24) =1124073478a(25) =2348810246a(26) =4898947078a(27) =10200547334a(28) =21206401030a(29) =44023414790