Number of 4-compositions of n.

Terms

a(0) =1a(1) =4a(2) =26a(3) =164a(4) =1031a(5) =6480a(6) =40728a(7) =255984a(8) =1608914a(9) =10112368a(10) =63558392a(11) =399478064a(12) =2510804924a(13) =15780945024a(14) =99186608832a(15) =623409013632