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: 1

Author

Amarnath Murthy, Feb 22 2002

Keywords

• base
• nonn

Examples

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

Crossrefs

Cf. A000217, A345110.

Programs

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 *)

Extensions

Edited by Robert G. Wilson v, Feb 28 2002

Offset changed by Andrew Howroyd, Sep 17 2024