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A110304 Least alternating multiple of alternators. 5
1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 121, 12, 52, 14, 30, 16, 34, 18, 38, 0, 21, 418, 23, 72, 25, 52, 27, 56, 29, 30, 341, 32, 165, 34, 70, 36, 74, 38, 78, 0, 41, 210, 43, 616, 45, 92, 47, 96, 49, 50, 561, 52, 212, 54, 165, 56, 456, 58, 236, 0, 61, 434, 63, 256, 65, 858, 67, 272, 69 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

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

Table of n, a(n) for n=1..69.

45th International Mathematical Olympiad (45th IMO), Problem #6 and Solution, Mathematics Magazine, 2005, Vol. 78, No. 3, pp. 247, 250-251.

EXAMPLE

a(11) = 121 because 121 is the least multiple of 11 which is alternating.

CROSSREFS

Cf. A030141, A110303, A110305.

Sequence in context: A258373 A250266 A085908 * A043315 A044912 A061378

Adjacent sequences:  A110301 A110302 A110303 * A110305 A110306 A110307

KEYWORD

base,easy,nonn

AUTHOR

Walter Nissen, Jul 18 2005

STATUS

approved

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Last modified June 21 19:59 EDT 2021. Contains 345365 sequences. (Running on oeis4.)