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A062691
Triangular numbers that contain exactly 2 different digits.
11
10, 15, 21, 28, 36, 45, 78, 91, 171, 300, 595, 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, 2222211111, 5000050000
OFFSET
1,1
COMMENTS
For n > 2, A309597(n) is a term. - Seiichi Manyama, Sep 15 2019
LINKS
EXAMPLE
300 is triangular and contains the digits 0 and 3.
MATHEMATICA
Select[Accumulate[Range[14000]], Count[DigitCount[#], Except[0]]==2&] (* Harvey P. Dale, Nov 27 2011 *)
PROG
(PARI) for(k=0, 1e5, if(#Set(digits(j=k*(k+1)/2))==2, print1(j", "))) \\ Seiichi Manyama, Sep 15 2019
CROSSREFS
Cf. A000217, A045914 (all digits the same), A213516, A213518, A309597.
Sequence in context: A098564 A168103 A322045 * A257630 A129496 A075520
KEYWORD
base,easy,nonn
AUTHOR
Erich Friedman, Jul 04 2001
STATUS
approved