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Search: id:A110303
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| 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75
(list; graph; listen)
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OFFSET
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0,2
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COMMENT
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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.
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REFERENCES
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45th International Mathematical Olympiad (45th IMO), Problem #6 and Solution, Mathematics Magazine, 2005, Vol. 78, No. 3, pp. 247, 250-251.
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LINKS
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Walter Nissen, Home Page (listed in lieu of email address)
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FORMULA
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positive n, not congruent to 0 mod 20
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EXAMPLE
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11 is an alternator and in the sequence because it has a multiple which is
alternating. The least of these multiples is 121.
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CROSSREFS
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Cf. A030141, A110304, A110305.
Sequence in context: A096105 A051108 A051107 this_sequence A084981 A078453 A052425
Adjacent sequences: A110300 A110301 A110302 this_sequence A110304 A110305 A110306
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KEYWORD
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base,easy,nonn
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AUTHOR
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Walter Nissen Jul 18 2005
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