A069697 Triangular numbers with internal digits 5.

0, 1, 3, 6, 10, 15, 21, 28, 36, 45, 55, 66, 78, 91, 153, 253, 351, 2556, 6555

Offset: 1

Author

Amarnath Murthy, Apr 06 2002

Keywords

• nonn
• base
• fini
• full

Comments

For proof of finiteness see A069693.

Crossrefs

Cf. A069675 to A069684, A069693 to A069700.

Programs

Mathematica

Do[ If[ Union[ Drop[ RotateLeft[ IntegerDigits[n(n + 1)/2]], -2]] == {5}, Print[n(n + 1)/2]], {n, 14, 2 10^6}]
Select[Accumulate[Range[0,300]],IntegerLength[#]<3||Union[Most[Rest[IntegerDigits[#]]]]=={5}&] (* Harvey P. Dale, Aug 13 2025 *)

Extensions

Extended by Robert G. Wilson v, Apr 07 2002