a(n) = 2*a(n-1) + 4*a(n-2) - 2*a(n-3) with initial terms 1, 4, 13.

Terms

a(0) =1a(1) =4a(2) =13a(3) =40a(4) =124a(5) =382a(6) =1180a(7) =3640a(8) =11236a(9) =34672a(10) =107008a(11) =330232a(12) =1019152a(13) =3145216a(14) =9706576a(15) =29955712a(16) =92447296a(17) =285304288a(18) =880486336a(19) =2717295232a(20) =8385927232a(21) =25880062720a(22) =79869243904a(23) =246486884224a(24) =760690618624