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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
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.
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
KEYWORD
nonn,base
AUTHOR
EXTENSIONS
Corrected by N. J. A. Sloane, Sep 13 2019
STATUS
approved