a(n) = T(n,3), array T as in A049600.

Terms

a(0) =0a(1) =1a(2) =5a(3) =19a(4) =63a(5) =192a(6) =552a(7) =1520a(8) =4048a(9) =10496a(10) =26624a(11) =66304a(12) =162560a(13) =393216a(14) =940032a(15) =2224128a(16) =5214208a(17) =12124160a(18) =27983872a(19) =64159744a(20) =146210816a(21) =331350016a(22) =747110400a(23) =1676673024a(24) =3746562048a(25) =8338276352a(26) =18488492032