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A031962 Numbers with exactly three distinct base-10 digits.

%I A031962 #26 Aug 10 2021 18:46:27
%S A031962 102,103,104,105,106,107,108,109,120,123,124,125,126,127,128,129,130,
%T A031962 132,134,135,136,137,138,139,140,142,143,145,146,147,148,149,150,152,
%U A031962 153,154,156,157,158,159,160,162,163,164,165,167,168,169,170,172,173,174
%N A031962 Numbers with exactly three distinct base-10 digits.
%H A031962 Robert Israel, <a href="/A031962/b031962.txt">Table of n, a(n) for n = 1..10000</a> (first 648 terms from T. D. Noe)
%p A031962 f:= proc(d,b)  uses combinat; local S,Res,A1,A1p,A2,x1,x2;
%p A031962      Res:= NULL:
%p A031962      for S in choose({$0..b-1},3) do
%p A031962        x1:= S[3]*(b^d-1)/(b-1);
%p A031962        for A1 in powerset(d) minus {{}} do
%p A031962          if S[1]=0 and member(d,A1) then next fi;
%p A031962          x2:= x1 + (S[1]-S[3])*add(b^(j-1),j=A1);
%p A031962          A1p:= {$1..d} minus A1;
%p A031962          for A2 in powerset(A1p) minus {{},A1p} do
%p A031962            Res:= Res, x2 + (S[2]-S[3])*add(b^(j-1),j=A2);
%p A031962          od
%p A031962        od
%p A031962      od;
%p A031962      op(sort([Res]));
%p A031962 end proc:
%p A031962 f(3,10),f(4,10); # _Robert Israel_, Oct 29 2018
%t A031962 Select[Range[100, 200], Length[Union[IntegerDigits[#]]] == 3 &] (* _T. D. Noe_, Dec 04 2012 *)
%t A031962 Select[Range[100,200],Count[DigitCount[#],0]==7&] (* _Harvey P. Dale_, May 22 2020 *)
%o A031962 (PARI) isok(n) = #Set(digits(n)) == 3; \\ _Michel Marcus_, Oct 29 2018
%Y A031962 Cf. A031956, A031957, A031958, A031959, A031960, A031961.
%K A031962 nonn,base
%O A031962 1,1
%A A031962 _Clark Kimberling_
%E A031962 Edited by _Robert Israel_, Oct 29 2018