Left half of trinomial triangle (A027907), triangle read by rows.

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =2a(5) =3a(6) =1a(7) =3a(8) =6a(9) =7a(10) =1a(11) =4a(12) =10a(13) =16a(14) =19a(15) =1a(16) =5a(17) =15a(18) =30a(19) =45a(20) =51a(21) =1a(22) =6a(23) =21a(24) =50a(25) =90a(26) =126a(27) =141a(28) =1a(29) =7