a(n) = 2*a(n-1) + 2*a(n-2) for n > 1; a(0)=2, a(1)=2.

Terms

a(0) =2a(1) =2a(2) =8a(3) =20a(4) =56a(5) =152a(6) =416a(7) =1136a(8) =3104a(9) =8480a(10) =23168a(11) =63296a(12) =172928a(13) =472448a(14) =1290752a(15) =3526400a(16) =9634304a(17) =26321408a(18) =71911424a(19) =196465664a(20) =536754176a(21) =1466439680a(22) =4006387712a(23) =10945654784a(24) =29904084992a(25) =81699479552a(26) =223207129088a(27) =609813217280