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A069693 Triangular numbers with either no internal digits or all internal digits are 0. 8
0, 1, 3, 6, 10, 15, 21, 28, 36, 45, 55, 66, 78, 91, 105, 300, 406, 703, 903, 3003, 4005, 8001 (list; graph; refs; listen; history; text; internal format)
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

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Last modified September 25 21:33 EDT 2017. Contains 292500 sequences.