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 A110305 Factors of alternators which produce least alternating multiples. 3
 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 11, 1, 4, 1, 2, 1, 2, 1, 2, 0, 1, 19, 1, 3, 1, 2, 1, 2, 1, 1, 11, 1, 5, 1, 2, 1, 2, 1, 2, 0, 1, 5, 1, 14, 1, 2, 1, 2, 1, 1, 11, 1, 4, 1, 3, 1, 8, 1, 4, 0, 1, 7, 1, 4, 1, 13, 1, 4, 1, 1, 11, 1, 4, 1, 6, 1, 5, 1, 6, 0, 1, 5, 1, 3, 1, 3, 1, 7, 1, 1, 12, 1, 18, 1, 23, 1, 34, 1, 111, 0 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,11 COMMENTS An alternating integer is a positive integer for which, in base-10, the parity of its digits alternates. E.g. 121 is alternating because its consecutive digits are odd-even-odd, 1 being odd and 2 even. Of course, 1234567890 is also alternating. An alternator is a positive integer which has a multiple which is alternating. For n congruent to 0 mod 20, a(n) is shown as zero to indicate that n is not an alternator. LINKS 45th International Mathematical Olympiad (45th IMO), Problem #6 and Solution, Mathematics Magazine, 2005, Vol. 78, No. 3, pp. 247, 250-251. EXAMPLE a(13) is 4 because the least multiple of 13 which is alternating is 52, which is 13 * 4. Of course 13, 26 and 39 are not alternating. 52 is alternating because 5 is odd and 2 is even. CROSSREFS Cf. A030141, A110303, A110304. Sequence in context: A010198 A204846 A127991 * A010199 A010200 A086320 Adjacent sequences:  A110302 A110303 A110304 * A110306 A110307 A110308 KEYWORD base,easy,nonn AUTHOR Walter Nissen, Jul 18 2005 STATUS approved

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