A069693 Triangular numbers with either no internal digits or all internal digits are 0.

0, 1, 3, 6, 10, 15, 21, 28, 36, 45, 55, 66, 78, 91, 105, 300, 406, 703, 903, 3003, 4005, 8001

Offset

1,3

Links

Table of n, a(n) for n=1..22.

Max Alekseyev, Proof of finiteness of A069693 - A069700

Example

The internal digits of 3003 are "00", which are both 0. 15 has no internal digits.

Mathematica

Do[ If[ Union[ Drop[ RotateLeft[ IntegerDigits[n(n + 1)/2]], -2]] == {0}, Print[n(n + 1)/2]], {n, 14, 2 10^6}]

Crossrefs

Cf. A069675-A069684, A069693-A069700.

Sequence in context: A077367 A077366 A077368 * A069694 A069695 A069697

Adjacent sequences: A069690 A069691 A069692 * A069694 A069695 A069696

Keyword

nonn,base,fini,full

Author

Amarnath Murthy, Apr 06 2002

Extensions

Corrected by Sascha Kurz, Jan 02 2003

Status

approved