cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

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A338338 Lexicographically earliest infinite sequence of distinct positive numbers such that for any prime p, any run of consecutive multiples of p has length exactly 3.

Original entry on oeis.org

1, 2, 4, 6, 3, 9, 5, 10, 20, 8, 7, 14, 28, 12, 15, 30, 40, 16, 11, 22, 44, 18, 21, 42, 56, 24, 27, 33, 55, 110, 50, 26, 13, 39, 36, 48, 32, 17, 34, 68, 38, 19, 57, 45, 60, 70, 84, 63, 51, 85, 170, 80, 46, 23, 69, 54, 66, 88, 77, 35, 105, 75, 72, 52, 78, 117
Offset: 1

Views

Author

N. J. A. Sloane, Oct 27 2020

Keywords

Comments

If a prime p divides a(n), then there is a run of exactly three terms (one of which is a(n)) that are divisible by p.
If "three" is changed to "two", we get A280864.
Conjecture: This is a permutation of the positive integers.

Examples

			After 1,2,4,6,3, we have had two successive multiples of 3, so the next term must be a multiple of 3 we have not yet seen, hence 9. The following term is then the smallest number not yet seen which is not a multiple of 3, hence 5.

Links

Crossrefs

A338339-A338349, A338440, A338449, A338450, and A338451 analyze this sequence from various points of view.
Cf. A280864, A338441.

Programs

  • PARI
    See Links section.

Extensions

Corrected and extended by Rémy Sigrist, Oct 27 2020
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Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

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