T(n,3) of A086350.

Terms

a(0) =1a(1) =4a(2) =17a(3) =74a(4) =325a(5) =1432a(6) =6317a(7) =27878a(8) =123049a(9) =543148a(10) =2397545a(11) =10583234a(12) =46716589a(13) =206216896a(14) =910285253a(15) =4018193246a(16) =17737162705a(17) =78295623508a(18) =345613602113