Row 3 of rectangular table A124460.

Terms

a(0) =1a(1) =4a(2) =13a(3) =44a(4) =162a(5) =637a(6) =2622a(7) =11188a(8) =49293a(9) =223768a(10) =1044661a(11) =5006126a(12) =24580704a(13) =123464593a(14) =633467893a(15) =3315948760a(16) =17690431736a(17) =96101620364a(18) =531196784996