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

Terms

a(0) =-1a(1) =2a(2) =3a(3) =8a(4) =19a(5) =46a(6) =111a(7) =268a(8) =647a(9) =1562a(10) =3771a(11) =9104a(12) =21979a(13) =53062a(14) =128103a(15) =309268a(16) =746639a(17) =1802546a(18) =4351731a(19) =10506008a(20) =25363747a(21) =61233502a(22) =147830751a(23) =356895004a(24) =861620759a(25) =2080136522a(26) =5021893803a(27) =12123924128a(28) =29269742059a(29) =70663408246