A062691 Triangular numbers that contain exactly 2 different digits.

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

Seiichi Manyama, Table of n, a(n) for n = 1..51

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

Adjacent sequences: A062688 A062689 A062690 * A062692 A062693 A062694

Keyword

base,easy,nonn

Author

Erich Friedman, Jul 04 2001

Status

approved