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 A326894 a(1) = 1; thereafter, a(n) is the reversal of the next prime after a(n - 1) in base 3 if n is prime, and the reversal of the next composite after a(n - 1) in base 3 if n is composite. 6
 1, 2, 1, 4, 7, 8, 19, 20, 5, 2, 1, 4, 7, 8, 1, 4, 7, 8, 19, 20, 5, 2, 1, 4, 2, 4, 2, 4, 7, 8, 19, 20, 5, 2, 4, 2, 1, 4, 2, 4, 7, 8, 19, 20, 5, 2, 1, 4, 2, 4, 2, 4, 7, 8, 1, 4, 2, 4, 7, 8, 19, 20, 5, 2, 4, 2, 1, 4, 2, 4, 7, 8, 19, 20, 5, 2, 4, 2, 1, 4, 2, 4, 7, 8, 1, 4, 2, 4, 7, 8, 1, 4, 2 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS The sequence is written in base 10. Rémy Sigrist's argument from A326344 gives an upper bound of 23, although the true maximum value is 20, as confirmed by Andrew Weimholt's argument from A326344. LINKS N. J. A. Sloane, Table of n, a(n) for n = 1..20000 Robert Dougherty-Bliss, Proof that A326894 is bounded with maximum value 20 EXAMPLE By definition, a(1) = 1. The next composite after a(3) = 1 is 4, or 11 in base 3. Reversed this is still 11 in base 3, or 4 in base 10. Thus a(4) = 4 since 4 is composite. CROSSREFS Cf. A326344, A326892, A151800, A113646. Sequence in context: A358566 A139769 A357470 * A275778 A007839 A364658 Adjacent sequences: A326891 A326892 A326893 * A326895 A326896 A326897 KEYWORD nonn,base AUTHOR Robert Dougherty-Bliss, Sep 13 2019 EXTENSIONS Corrected by N. J. A. Sloane, Sep 13 2019 STATUS approved

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Last modified April 23 13:51 EDT 2024. Contains 371914 sequences. (Running on oeis4.)