This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A094045 #2 Mar 30 2012 17:31:00
%S A094045 1,3,49,19,9,7,27,11,51,13,21,29,39,17,33,23,57,37,69,47,87,31,63,43,
%T A094045 91,61,99,41,77,53,81,67,93,71,119,59,123,73,121,97,117,79,111,103,
%U A094045 141,101,159,113,143,89,153,83,177,109,133,157,189,127,207,139,169,151,171,131
%N A094045 Alternate composite and prime numbers not included earlier such that every concatenation of a pair of terms is a prime: a(2n) is prime and a(2n-1) is nonprime.
%C A094045 Conjecture: 2 and 5 are the only two nonmembers.
%e A094045 a(3)=49 => 349 is a prime but not necessarily 1349, which by the way it
%e A094045 is not.
%t A094045 p = Prime[ Range[ 500]]; np = Drop[ Complement[ Range[ 500], p], 1]; a[1] = 1; a[n_] := a[n] = Block[{k = 1, q = IntegerDigits[a[n - 1]]}, If[ EvenQ[n], While[ !PrimeQ[ FromDigits[ Join[q, IntegerDigits[ p[[k]] ]]]], k++ ]; q = p[[k]]; p = Delete[p, k]; q, While[ !PrimeQ[ FromDigits[ Join[q, IntegerDigits[ np[[k]] ]]]], k++ ]; q = np[[k]]; np = Delete[np, k]; q]]; Table[ a[n], {n, 60}]
%Y A094045 Cf. A094043, A094044.
%K A094045 nonn,base
%O A094045 1,2
%A A094045 _Robert G. Wilson v_, Apr 23 2004