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%I #32 Jun 09 2022 21:49:31
%S 9,91,913,9131,91311,913111,9131111,91311111,913111111,9131111111,
%T 91311111111,913111111113,9131111111131,91311111111311,
%U 913111111113111,9131111111131111,91311111111311111,913111111113111111,9131111111131111111,91311111111311111111
%N a(n) is the smallest composite number ending in 1, 3, 7, or 9 with n digits whose first n-1 digits are a(n-1).
%C Question: do only a finite number of terms end in a digit other than 1?
%C Question: is the sequence infinite?
%e 911 is not a(3) because 911 is prime.
%o (PARI) lista(nn) = {vi = [1, 3, 7, 9]; a = 9; print1(a, ", "); for (n=1, nn, ok = 0; for (i=1, #vi, if (!isprime(na = eval(concat(Str(a), Str(vi[i])))), ok = 1; break;);); if (!ok, print("end of sequence"); return();); a = na; print1(a, ", "););} \\ _Michel Marcus_, May 11 2014
%K nonn,base
%O 1,1
%A _J. Lowell_, May 10 2014
%E More terms from _Michel Marcus_, May 11 2014
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