Triangular numbers whose reverse is also triangular.

Terms

a(0) =1a(1) =3a(2) =6a(3) =55a(4) =66a(5) =153a(6) =171a(7) =351a(8) =595a(9) =666a(10) =3003a(11) =5995a(12) =8778a(13) =15051a(14) =17578a(15) =66066a(16) =87571a(17) =185745a(18) =547581a(19) =617716a(20) =828828a(21) =1269621a(22) =1461195a(23) =1680861a(24) =3544453a(25) =5073705a(26) =5676765a(27) =5911641a(28) =6295926a(29) =12145056