Triangular numbers with at most two distinct prime factors.

Terms

a(0) =1a(1) =3a(2) =6a(3) =10a(4) =15a(5) =21a(6) =28a(7) =36a(8) =45a(9) =55a(10) =91a(11) =136a(12) =153a(13) =171a(14) =253a(15) =325a(16) =351a(17) =496a(18) =703a(19) =1081a(20) =1225a(21) =1431a(22) =1711a(23) =1891a(24) =2701a(25) =3321a(26) =3403a(27) =4753a(28) =5671a(29) =7381