a(n) = 11*2^n - 4*n - 10.

Terms

a(0) =1a(1) =8a(2) =26a(3) =66a(4) =150a(5) =322a(6) =670a(7) =1370a(8) =2774a(9) =5586a(10) =11214a(11) =22474a(12) =44998a(13) =90050a(14) =180158a(15) =360378a(16) =720822a(17) =1441714a(18) =2883502a(19) =5767082a(20) =11534246a(21) =23068578a(22) =46137246a(23) =92274586a(24) =184549270a(25) =369098642a(26) =738197390a(27) =1476394890a(28) =2952789894a(29) =5905579906