a(n) = 42*2^n - 20.

Terms

a(0) =22a(1) =64a(2) =148a(3) =316a(4) =652a(5) =1324a(6) =2668a(7) =5356a(8) =10732a(9) =21484a(10) =42988a(11) =85996a(12) =172012a(13) =344044a(14) =688108a(15) =1376236a(16) =2752492a(17) =5505004a(18) =11010028a(19) =22020076a(20) =44040172a(21) =88080364a(22) =176160748a(23) =352321516a(24) =704643052a(25) =1409286124a(26) =2818572268a(27) =5637144556a(28) =11274289132a(29) =22548578284