A067269 Triangular numbers which remain triangular when the most significant digit is moved to the end.

1, 3, 6, 10, 55, 66, 300, 325, 666, 1035, 1485, 1891, 61776, 103740, 109746, 112575, 190653, 340725, 1026028, 1264845, 3000025, 3002475, 3592540, 3670695, 37840650, 60000535, 61577253, 65008503, 1001393128, 1432436050, 1560756385

Offset

0,2

Links

Table of n, a(n) for n=0..30.

Example

1485 is a term as 1485 and 4851 both are triangular numbers.

Mathematica

Do[k = FromDigits[ RotateLeft[ IntegerDigits[n(n + 1)/2]]]; l = Floor[ Sqrt[2k]]; If[k == l(l + 1)/2, Print[n(n + 1)/2]], {n, 1, 10^5}]
msdmeQ[n_]:=IntegerQ[(Sqrt[1+8*FromDigits[RotateLeft[IntegerDigits[ n]]]]-1)/2]; Select[Accumulate[Range[55900]], msdmeQ] (* Harvey P. Dale, Aug 22 2014 *)

Crossrefs

Sequence in context: A069708 A061455 A068071 * A352057 A343811 A071299

Adjacent sequences: A067266 A067267 A067268 * A067270 A067271 A067272

Keyword

base,nonn

Author

Amarnath Murthy, Feb 22 2002

Extensions

Edited by Robert G. Wilson v, Feb 28 2002

Status

approved