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a(1) = 9. For n > 1, a(n) is the least unused number such that the decimal concatenation a(n)a(n-1)...a(2)a(1) is prime.
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%I #10 Jan 22 2022 08:47:26

%S 9,1,4,5,3,7,12,11,13,42,26,10,17,16,20,82,29,78,57,27,28,66,45,6,69,

%T 33,236,40,116,237,196,65,133,90,60,72,80,61,126,24,153,68,88,122,43,

%U 156,231,285,125,177,249,106,36,147,23,208,483,138,281,63,108,22,38,75,159

%N a(1) = 9. For n > 1, a(n) is the least unused number such that the decimal concatenation a(n)a(n-1)...a(2)a(1) is prime.

%C Is this a permutation of the positive integers?

%C The sequence is infinite by Dirichlet's theorem; Linnik's theorem gives an effectively computable bound on its members. Using Xylouris's version with L <= 5.2, a(n) = 9^(5.2^(n + O(log n))). - _Charles R Greathouse IV_, Apr 27 2010

%Y Cf. A089710, A089711, A089560-A089573.

%K nonn,base

%O 1,1

%A _Ray Chandler_, Nov 22 2003