Palindromic triangular numbers.

Terms

a(0) =0a(1) =1a(2) =3a(3) =6a(4) =55a(5) =66a(6) =171a(7) =595a(8) =666a(9) =3003a(10) =5995a(11) =8778a(12) =15051a(13) =66066a(14) =617716a(15) =828828a(16) =1269621a(17) =1680861a(18) =3544453a(19) =5073705a(20) =5676765a(21) =6295926a(22) =35133153a(23) =61477416a(24) =178727871a(25) =1264114621a(26) =1634004361a(27) =5289009825a(28) =6172882716a(29) =13953435931