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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.
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%I #10 Sep 29 2019 00:26:17

%S 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,

%T 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,

%U 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

%N 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.

%C The sequence is written in base 10.

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

%H Robert Israel, <a href="/A327464/b327464.txt">Table of n, a(n) for n = 1..10000</a>

%p digrev:= proc(n) local L,i;

%p L:= convert(n,base,5);

%p add(L[-i]*5^(i-1),i=1..nops(L))

%p end proc:

%p nextcomp:= proc(n) local m;

%p for m from n+1 do if not isprime(m) then return m fi od

%p end proc:

%p A[1]:= 1:

%p for n from 2 to 100 do

%p if isprime(n) then A[n]:= digrev(nextprime(A[n-1]))

%p else A[n]:= digrev(nextcomp(A[n-1]))

%p fi

%p od:

%p seq(A[i],i=1..100); # _Robert Israel_, Sep 28 2019

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

%K nonn,base

%O 1,2

%A _N. J. A. Sloane_, Sep 27 2019