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 A031959 Numbers with exactly three distinct base-7 digits. 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 Cf. A007093. 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 May 24 15:14 EDT 2024. Contains 372778 sequences. (Running on oeis4.)