Number of binary codes (not necessarily linear) of length n with 4 words.

Terms

a(0) =0a(1) =1a(2) =6a(3) =19a(4) =47a(5) =103a(6) =203a(7) =373a(8) =649a(9) =1079a(10) =1727a(11) =2681a(12) =4048a(13) =5969a(14) =8620a(15) =12218a(16) =17028a(17) =23378a(18) =31654a(19) =42324a(20) =55941a(21) =73155a(22) =94725