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A213516
Triangular numbers having only 1 or 2 different digits in base 10.
8
0, 1, 3, 6, 10, 15, 21, 28, 36, 45, 55, 66, 78, 91, 171, 300, 595, 666, 990, 1711, 2211, 3003, 5050, 5151, 5565, 5995, 6555, 8778, 10011, 66066, 222111, 255255, 333336, 500500, 600060, 828828, 887778, 1188111, 5656566, 22221111, 50005000, 51151555, 88877778
OFFSET
1,3
COMMENTS
The list of triangular numbers containing only one digit (A045914) is finite. This list is infinite because numbers like 8888777778, 222222111111, and 500000500000 occur an infinite number of times.
A309597 is a subsequence. - Seiichi Manyama, Sep 14 2019
LINKS
MATHEMATICA
t = {}; Do[tri = n*(n+1)/2; If[Length[Union[IntegerDigits[tri]]] <= 2, AppendTo[t, tri]], {n, 0, 10^5}]; t
Select[Accumulate[Range[0, 20000]], Count[DigitCount[#], 0]>7&] (* Harvey P. Dale, Sep 03 2020 *)
PROG
(Magma) [n*(n+1)/2: n in [0..10^5] | #Set(Intseq(n*(n+1) div 2)) le 2]; // Bruno Berselli, Oct 27 2012
CROSSREFS
Cf. A119033 (has list of sequences related to digits in triangular numbers).
Sequence in context: A069695 A069697 A069699 * A078254 A069700 A069698
KEYWORD
nonn,base
AUTHOR
T. D. Noe, Jun 21 2012
STATUS
approved