Nontrivial trinomial coefficients.

Terms

a(0) =1a(1) =3a(2) =6a(3) =7a(4) =10a(5) =15a(6) =16a(7) =19a(8) =21a(9) =28a(10) =30a(11) =36a(12) =45a(13) =50a(14) =51a(15) =55a(16) =66a(17) =77a(18) =78a(19) =90a(20) =91a(21) =105a(22) =112a(23) =120a(24) =126a(25) =136a(26) =141a(27) =153a(28) =156a(29) =161