A110305 Factors of alternators which produce least alternating multiples.

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

Offset: 1

Author

Walter Nissen, Jul 18 2005

Keywords

• base
• easy
• nonn

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.

Examples

			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.
		

Links

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

Crossrefs

Cf. A030141, A110303, A110304.