Triangle read by rows: 3-Stirling numbers of the second kind.

Terms

a(0) =1a(1) =3a(2) =1a(3) =9a(4) =7a(5) =1a(6) =27a(7) =37a(8) =12a(9) =1a(10) =81a(11) =175a(12) =97a(13) =18a(14) =1a(15) =243a(16) =781a(17) =660a(18) =205a(19) =25a(20) =1a(21) =729a(22) =3367a(23) =4081a(24) =1890a(25) =380a(26) =33a(27) =1a(28) =2187a(29) =14197