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%I #15 Dec 20 2017 14:42:05
%S 4,6,8,9,10,12,15,20,21,22,25,27,30,32,33,35,50,51,52,55,57,70,72,75,
%T 77,111,117,171,371,711,713,731
%N Minimal set of composite-strings in base 10.
%C Any composite number contains in its digits at least one of the term of this sequence and there is no smaller set.
%D J.-P. Delahaye, "Pour la science", (French edition of Scientific American), Juin 2002, p. 99
%D J. Shallit, Minimal primes, in J.Recreational Mathematics, vol. 30.2, pp. 113-117,1999-2000
%H J. Shallit, <a href="http://www.cs.uwaterloo.ca/~shallit/Papers/minimal5.ps">Minimal primes</a>, J. Recreational Mathematics, vol. 30.2, pp. 113-117, 1999-2000.
%t subs[digits_List] := Select[Subsets[digits], CompositeQ[FromDigits[#]]&] //. {a___List, b_List, c___List, d_List, e___List} /; MemberQ[Subsets[d], b] :> {a, b, c, e};
%t aa = {};
%t Do[aa = Union[aa, subs[IntegerDigits[n]]], {n, Select[Range[1000], CompositeQ]}];
%t A071070 = FromDigits /@ aa (* _Jean-François Alcover_, Dec 20 2017 *)
%Y Cf. A071062, A071071, A071072, A071073.
%K fini,full,nice,nonn,base
%O 1,1
%A _Benoit Cloitre_, May 26 2002
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