A327464 a(1) = 1; thereafter, a(n) is the reversal of the next prime after a(n - 1) in base 5 if n is prime, and the reversal of the next composite after a(n - 1) in base 5 if n is composite.

1, 2, 3, 4, 1, 4, 1, 4, 6, 16, 13, 22, 19, 4, 6, 16, 13, 22, 19, 4, 6, 16, 13, 22, 24, 1, 4, 6, 11, 12, 17, 18, 4, 6, 16, 18, 23, 24, 1, 4, 1, 4, 1, 4, 6, 16, 13, 22, 24, 1, 4, 6, 11, 12, 22, 24, 1, 4, 1, 4, 1, 4, 6, 16, 18, 4, 1, 4, 6, 16, 13, 22, 19, 4, 6, 16, 18, 4, 1, 4, 6, 16, 13, 22, 24

Offset

1,2

Comments

The sequence is written in base 10.

Conjecture: the maximal value is 107, first attained at n = 883.

Links

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

Maple

digrev:= proc(n) local L, i;
  L:= convert(n, base, 5);
  add(L[-i]*5^(i-1), i=1..nops(L))
end proc:
nextcomp:= proc(n) local m;
  for m from n+1 do if not isprime(m) then return m fi od
end proc:
A[1]:= 1:
for n from 2 to 100 do
  if isprime(n) then A[n]:= digrev(nextprime(A[n-1]))
  else A[n]:= digrev(nextcomp(A[n-1]))
  fi
od:
seq(A[i], i=1..100); # Robert Israel, Sep 28 2019

Crossrefs

For bases 3,5,6,7,10 see A326894, A327464 = the present sequence, A327463, A327241, A326344.

Sequence in context: A280694 A270313 A343251 * A318308 A003324 A110630

Adjacent sequences: A327461 A327462 A327463 * A327465 A327466 A327467

Keyword

nonn,base

Author

N. J. A. Sloane, Sep 27 2019

Status

approved