A327241 a(1) = 1. Thereafter, if n is prime, a(n) is the next prime after a(n-1), but written backwards in base 7; if n is composite, a(n) is the next composite after a(n-1), written backwards in base 7.

1, 2, 3, 4, 5, 6, 1, 4, 6, 8, 29, 18, 37, 26, 45, 34, 19, 44, 41, 6, 8, 15, 23, 24, 31, 32, 39, 40, 47, 48, 197, 102, 296, 153, 10, 36, 19, 44, 27, 4, 5, 6, 1, 4, 6, 8, 29, 18, 44, 27, 4, 6, 1, 4, 6, 8, 15, 16, 23, 24, 11, 36, 26, 45, 34, 5, 1, 4, 6, 8, 29, 18

Offset

1,2

Comments

The sequence is written in base 10.

Rémy Sigrist's and Andrew Weimholt's methods from A326344 both show that a(n) <= 314, but the true maximum is 310. This can be shown by adapting Weimholt's argument to use values of n mod 30 rather than n mod 6.

Links

Robert Israel, Table of n, a(n) for n = 1..10000

Example

a(1) = 1 by definition. The next prime after a(6) = 6 is 7_10 = 10_7, so a(7) = 1_7 = 1_10 since 7 is prime.

Maple

A:= Vector(100):
A[1]:= 1:
for n from 2 to 100 do
  if isprime(n) then
    r:= nextprime(A[n-1])
  else
    for r from A[n-1]+1 while isprime(r) do od
  fi;
  A[n]:= revdigs(r)
od:
convert(A, list); # Robert Israel, Mar 23 2021

Crossrefs

Cf. A326344, A326894.

Sequence in context: A337223 A125934 A125935 * A316913 A319092 A243733

Adjacent sequences: A327238 A327239 A327240 * A327242 A327243 A327244

Keyword

base,nonn,look

Author

Robert Dougherty-Bliss, Sep 14 2019

Status

approved