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 A154966 #16 Sep 08 2022 08:45:40
%S A154966 3,5,7,11,13,19,29,31,37,43,47,53,59,67,73,79,89,97,101,103,107,109,
%T A154966 113,131,137,139,149,151,157,163,167,173,179,181,191,193,197,199,211,
%U A154966 223,229,233,239,241,251,257,263,269,271,277,281,283,293,307,311,313,317
%N A154966 Primes p such that the concatenation of p and prime(p) is composite.
%H A154966 Harvey P. Dale, <a href="/A154966/b154966.txt">Table of n, a(n) for n = 1..1000</a>
%e A154966 The concatenation of prime 3 and the third prime, 5, is the composite 35, hence 3 is in the sequence.
%e A154966 The concatenation of prime 29 and the 29th prime, 109, is the composite 29109 = 3*31*313, hence 29 is in the sequence.
%t A154966 Select[Prime[Range[80]],CompositeQ[FromDigits[Flatten[IntegerDigits[ {#,Prime[ #]}]]]]&] (* _Harvey P. Dale_, Jan 07 2016 *)
%o A154966 (Magma) [ p: p in PrimesUpTo(320) | not IsPrime(StringToInteger(IntegerToString(p) cat IntegerToString(NthPrime(p)))) ];
%Y A154966 Cf. A000040 (primes), A002808 (composites), A045532.
%K A154966 nonn,base,easy,less
%O A154966 1,1
%A A154966 _Juri-Stepan Gerasimov_, Jan 18 2009
%E A154966 Edited and extended beyond a(6) by _Klaus Brockhaus_, Jan 20 2009