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A071070
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Minimal set of composite-strings in base 10.
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15
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4, 6, 8, 9, 10, 12, 15, 20, 21, 22, 25, 27, 30, 32, 33, 35, 50, 51, 52, 55, 57, 70, 72, 75, 77, 111, 117, 171, 371, 711, 713, 731
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listen;
history;
text;
internal format)
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OFFSET
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1,1
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COMMENTS
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Any composite number contains in its digits at least one of the term of this sequence and there is no smaller set.
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REFERENCES
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J.-P. Delahaye, "Pour la science", (French edition of Scientific American), Juin 2002, p. 99
J. Shallit, Minimal primes, in J.Recreational Mathematics, vol. 30.2, pp. 113-117,1999-2000
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LINKS
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Table of n, a(n) for n=1..32.
J. Shallit, Minimal primes, J. Recreational Mathematics, vol. 30.2, pp. 113-117, 1999-2000.
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MATHEMATICA
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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};
aa = {};
Do[aa = Union[aa, subs[IntegerDigits[n]]], {n, Select[Range[1000], CompositeQ]}];
A071070 = FromDigits /@ aa (* Jean-François Alcover, Dec 20 2017 *)
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CROSSREFS
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Cf. A071062, A071071, A071072, A071073.
Sequence in context: A248010 A067013 A141607 * A275722 A047820 A248807
Adjacent sequences: A071067 A071068 A071069 * A071071 A071072 A071073
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KEYWORD
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fini,full,nice,nonn,base
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AUTHOR
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Benoit Cloitre, May 26 2002
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STATUS
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approved
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