a(n) = A027113(n, n+4).

Terms

a(0) =16a(1) =59a(2) =155a(3) =352a(4) =738a(5) =1475a(6) =2861a(7) =5444a(8) =10232a(9) =19079a(10) =35395a(11) =65452a(12) =120786a(13) =222615a(14) =409965a(15) =754616a(16) =1388592a(17) =2554723a(18) =4699643a(19) =8644840a(20) =15901266a(21) =29247995a(22) =53796541a(23) =98948444a(24) =181995832a(25) =334743887a(26) =615691459a(27) =1132434708