a(n) = 3*a(n-1) + 4*a(n-2) - 2*a(n-3) with a(0)=0, a(1)=1, a(2)=2.

Terms

a(0) =0a(1) =1a(2) =2a(3) =10a(4) =36a(5) =144a(6) =556a(7) =2172a(8) =8452a(9) =32932a(10) =128260a(11) =499604a(12) =1945988a(13) =7579860a(14) =29524324a(15) =115000436a(16) =447938884a(17) =1744769748a(18) =6796063908a(19) =26471392948a(20) =103108894980a(21) =401620128916