Triangular numbers obtained as the concatenation of n and n+1.

Terms

a(0) =45a(1) =78a(2) =4950a(3) =5253a(4) =295296a(5) =369370a(6) =415416a(7) =499500a(8) =502503a(9) =594595a(10) =652653a(11) =760761a(12) =22542255a(13) =49995000a(14) =50025003a(15) =88278828a(16) =1033010331a(17) =1487714878a(18) =4999950000a(19) =5000250003a(20) =490150490151a(21) =499999500000a(22) =500002500003a(23) =509949509950