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
Seiichi Manyama, Table of n, a(n) for n = 1..55
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
KEYWORD
nonn,base
AUTHOR
T. D. Noe, Jun 21 2012
STATUS
approved