a(n+3) = 2*a(n+2) + 3*a(n+1) - a(n); with a(1) = 1, a(2) = 4, a(3) = 10.

Terms

a(0) =1a(1) =4a(2) =10a(3) =31a(4) =88a(5) =259a(6) =751a(7) =2191a(8) =6376a(9) =18574a(10) =54085a(11) =157516a(12) =458713a(13) =1335889a(14) =3890401a(15) =11329756a(16) =32994826a(17) =96088519a(18) =279831760a(19) =814934251a(20) =2373275263a(21) =6911521519a(22) =20127934576a(23) =58617158446a(24) =170706599101a(25) =497136738964