a(n) = 2^(n-1)*(7*n-12) + 7.

Terms

a(0) =1a(1) =2a(2) =11a(3) =43a(4) =135a(5) =375a(6) =967a(7) =2375a(8) =5639a(9) =13063a(10) =29703a(11) =66567a(12) =147463a(13) =323591a(14) =704519a(15) =1523719a(16) =3276807a(17) =7012359a(18) =14942215a(19) =31719431a(20) =67108871a(21) =141557767a(22) =297795591a(23) =624951303a(24) =1308622855a(25) =2734686215a(26) =5704253447a(27) =11878268935a(28) =24696061959a(29) =51271172103