login
A067269
Triangular numbers which remain triangular when the most significant digit is moved to the end.
1
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
1,2
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
KEYWORD
base,nonn
AUTHOR
Amarnath Murthy, Feb 22 2002
EXTENSIONS
Edited by Robert G. Wilson v, Feb 28 2002
Offset changed by Andrew Howroyd, Sep 17 2024
STATUS
approved