A326892 a(n) is the reversal of the next composite after a(n-1) if n is prime, otherwise it is the reversal of the next prime after a(n-1), starting with a(1) = 1.

1, 4, 6, 7, 8, 11, 21, 32, 73, 97, 89, 79, 8, 11, 31, 73, 47, 35, 63, 76, 97, 101, 201, 112, 311, 313, 713, 917, 819, 128, 921, 929, 739, 347, 943, 749, 57, 95, 79, 38, 93, 79, 8, 11, 31, 73, 47, 35, 73, 97, 101, 301, 203, 112, 311, 313, 713, 917, 819, 128

Offset

1,2

Comments

Inspired by A326344.

The sequence is not periodic but bounded: a(n) <= 994 = a(1658) = a(2112) = a(2412) = a(3110) = ... .

Links

Alois P. Heinz, Table of n, a(n) for n = 1..20000

Alois P. Heinz, Plot of the first 10^6 terms

Maple

c:= n-> (k-> `if`(isprime(k), c(k), k))(n+1):
a:= proc(n) option remember; `if`(n=1, 1,
      (s-> parse(cat(s[-i]$i=1..length(s))))(""||(
      `if`(isprime(n), c(a(n-1)), nextprime(a(n-1))))))
    end:
seq(a(n), n=1..100);

Crossrefs

Cf. A000040, A002808, A004086, A113646, A151800, A326344.

Sequence in context: A084395 A047291 A100349 * A047507 A024554 A078744

Adjacent sequences: A326889 A326890 A326891 * A326893 A326894 A326895

Keyword

nonn,look,base

Author

Alois P. Heinz, Sep 13 2019

Status

approved