f(n,n+3) where f is given in A034261.

Terms

a(0) =0a(1) =1a(2) =13a(3) =99a(4) =605a(5) =3289a(6) =16653a(7) =80444a(8) =375972a(9) =1715130a(10) =7681586a(11) =33913385a(12) =148018455a(13) =640049865a(14) =2746422525a(15) =11708971560a(16) =49647131160a(17) =209523969630a(18) =880668859590