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 A071070 Minimal set of composite-strings in base 10. 12
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Any composite number contains in its digits at least one of the term of this sequence and there is no smaller set. REFERENCES 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 LINKS J. Shallit, Minimal primes, J. Recreational Mathematics, vol. 30.2, pp. 113-117, 1999-2000. MATHEMATICA 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 *) CROSSREFS Cf. A071062, A071071, A071072, A071073. Sequence in context: A248010 A067013 A141607 * A275722 A047820 A248807 Adjacent sequences:  A071067 A071068 A071069 * A071071 A071072 A071073 KEYWORD fini,full,nice,nonn,base AUTHOR Benoit Cloitre, May 26 2002 STATUS approved

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Last modified January 17 07:49 EST 2018. Contains 297787 sequences.