Numbers n such that n concatenated with n+1 is triangular.

Terms

a(0) =4a(1) =7a(2) =49a(3) =52a(4) =295a(5) =369a(6) =415a(7) =499a(8) =502a(9) =594a(10) =652a(11) =760a(12) =2254a(13) =4999a(14) =5002a(15) =8827a(16) =10330a(17) =14877a(18) =49999a(19) =50002a(20) =490150a(21) =499999a(22) =500002a(23) =509949a(24) =3347109a(25) =4999999a(26) =5000002a(27) =6983470a(28) =24913494a(29) =49999999