a(n) = 3*2^n - 2*(-1)^n.

Terms

a(0) =1a(1) =8a(2) =10a(3) =26a(4) =46a(5) =98a(6) =190a(7) =386a(8) =766a(9) =1538a(10) =3070a(11) =6146a(12) =12286a(13) =24578a(14) =49150a(15) =98306a(16) =196606a(17) =393218a(18) =786430a(19) =1572866a(20) =3145726a(21) =6291458a(22) =12582910a(23) =25165826a(24) =50331646a(25) =100663298a(26) =201326590a(27) =402653186a(28) =805306366a(29) =1610612738