Third row of A113439.

Terms

a(0) =1a(1) =4a(2) =17a(3) =72a(4) =306a(5) =1305a(6) =5577a(7) =23858a(8) =102108a(9) =437080a(10) =1871065a(11) =8009866a(12) =34289712a(13) =146792138a(14) =628407994a(15) =2690174883a(16) =11516466985a(17) =49301256865a(18) =211055514017a(19) =903515089697