a(n) = a(n-1) + 3*a(n-2) -2*a(n-3) - 2*a(n-4), where a(0) = 1, a(1) = 4, a(2) = 9, a(3) = 16.

Terms

a(0) =1a(1) =4a(2) =9a(3) =16a(4) =33a(5) =55a(6) =104a(7) =171a(8) =307a(9) =502a(10) =873a(11) =1423a(12) =2424a(13) =3943a(14) =6623a(15) =10758a(16) =17893a(17) =29035a(18) =47952a(19) =77755a(20) =127755a(21) =207046a(22) =338897a(23) =549015a(24) =896104a(25) =1451263a(26) =2363751a(27) =3827302a(28) =6223821a(29) =10075699