Number of base 4 n-digit numbers with digit sum n.

Terms

a(0) =1a(1) =2a(2) =6a(3) =19a(4) =61a(5) =201a(6) =672a(7) =2269a(8) =7723a(9) =26452a(10) =91058a(11) =314766a(12) =1091884a(13) =3798900a(14) =13251136a(15) =46325285a(16) =162268775a(17) =569385098a(18) =2001012474a(19) =7042014879a(20) =24813529581a(21) =87533417037a(22) =309107111536