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A031959 Numbers in which the number of distinct base 7 digits is 3. 2
51, 52, 53, 54, 55, 63, 66, 67, 68, 69, 70, 72, 74, 75, 76, 77, 79, 80, 82, 83, 84, 86, 87, 88, 90, 91, 93, 94, 95, 96, 99, 101, 102, 103, 104, 105, 108, 109, 110, 111, 119, 120, 123, 124, 125, 126, 127, 129, 131, 132, 133, 134, 136 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

MAPLE

f:= proc(d)  uses combinat; local S, Res, A1, A1p, A2, x1, x2;

     Res:= NULL:

     for S in choose({$0..6}, 3) do

       x1:= S[3]*(7^d-1)/6;

       for A1 in powerset(d) minus {{}} do

         if S[1]=0 and member(d, A1) then next fi;

         x2:= x1 + (S[1]-S[3])*add(7^(j-1), j=A1);

         A1p:= {$1..d} minus A1;

         for A2 in powerset(A1p) minus {{}, A1p} do

           Res:= Res, x2 + (S[2]-S[3])*add(7^(j-1), j=A2);

         od

       od

     od;

     sort([Res]);

end proc:

op(f(3)), op(f(4)); # Robert Israel, Oct 29 2018

MATHEMATICA

Select[Range[150], Length[Union[IntegerDigits[#, 7]]]==3&] (* Harvey P. Dale, Mar 29 2019 *)

CROSSREFS

Sequence in context: A039932 A210183 A210086 * A144162 A169984 A042299

Adjacent sequences:  A031956 A031957 A031958 * A031960 A031961 A031962

KEYWORD

nonn,base

AUTHOR

Clark Kimberling

STATUS

approved

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Last modified March 28 05:38 EDT 2020. Contains 333073 sequences. (Running on oeis4.)