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a(1) = 1, a(n) = smallest composite number not occurring earlier such that the concatenation a(n-1) and a(n) is a prime.
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%I #5 Jan 08 2019 09:12:41

%S 1,9,77,27,49,33,91,51,133,39,119,69,143,21,121,57,203,93,169,63,247,

%T 81,299,147,209,123,217,87,187,111,253,153,259,99,289,129,221,159,161,

%U 141,301,177,319,117,329,201,287,219,361,183,343,237,581,171,341,273,323

%N a(1) = 1, a(n) = smallest composite number not occurring earlier such that the concatenation a(n-1) and a(n) is a prime.

%Y Cf. A075607, A075609, A075610.

%K base,nonn

%O 1,2

%A _Amarnath Murthy_, Sep 28 2002

%E More terms from _Michel ten Voorde_ Jun 23 2003