A068071 Triangular numbers that remain triangular when the least significant digit is moved to the beginning.

1, 3, 6, 10, 55, 66, 210, 253, 666, 780, 4851, 8911, 15400, 17766, 125751, 303810, 407253, 906531, 1125750, 2648451, 5925403, 6706953, 15772536, 22207780, 50085036, 78406503, 438094800, 1623331710, 1764803755, 3437158416

Offset

1,2

Links

Table of n, a(n) for n=1..30.

Example

8911 = A000217(133) is in the sequence because 8911 becomes 1891 which is A000217(61).

Mathematica

Do[k = FromDigits[ RotateRight[ IntegerDigits[n(n + 1)/2]]]; l = Floor[ Sqrt[2k]]; If[k == l(l + 1)/2, Print[n(n + 1)/2]], {n, 1, 10^5}]

Crossrefs

Cf. A000217, A067269.

Sequence in context: A160965 A069708 A061455 * A067269 A352057 A343811

Adjacent sequences: A068068 A068069 A068070 * A068072 A068073 A068074

Keyword

base,nonn

Author

Robert G. Wilson v, Feb 28 2002

Status

approved