OFFSET
1,1
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..1000
EXAMPLE
The concatenation of prime 3 and the third prime, 5, is the composite 35, hence 3 is in the sequence.
The concatenation of prime 29 and the 29th prime, 109, is the composite 29109 = 3*31*313, hence 29 is in the sequence.
MATHEMATICA
Select[Prime[Range[80]], CompositeQ[FromDigits[Flatten[IntegerDigits[ {#, Prime[ #]}]]]]&] (* Harvey P. Dale, Jan 07 2016 *)
PROG
(Magma) [ p: p in PrimesUpTo(320) | not IsPrime(StringToInteger(IntegerToString(p) cat IntegerToString(NthPrime(p)))) ];
CROSSREFS
KEYWORD
nonn,base,easy,less
AUTHOR
Juri-Stepan Gerasimov, Jan 18 2009
EXTENSIONS
Edited and extended beyond a(6) by Klaus Brockhaus, Jan 20 2009
STATUS
approved