OFFSET
1,2
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..1000
EXAMPLE
The concatenation of the nonprime 1 and the first prime 2 is the composite 12, hence 1 is in the sequence.
Concatenation of nonprime 9 and ninth prime 23 is the composite 923 = 13*71, hence 9 is in the sequence.
MATHEMATICA
Select[Range[120], !PrimeQ[#]&&CompositeQ[FromDigits[Join[ IntegerDigits[ #], IntegerDigits[ Prime[#]]]]]&] (* Harvey P. Dale, Mar 08 2018 *)
PROG
(Magma) [ n: n in [1..118] | not IsPrime(n) and not IsPrime(StringToInteger(IntegerToString(n) cat IntegerToString(NthPrime(n)))) ];
CROSSREFS
KEYWORD
nonn,base,easy,less
AUTHOR
Juri-Stepan Gerasimov, Jan 18 2009
EXTENSIONS
Edited and extended beyond a(12) by Klaus Brockhaus, Jan 20 2009
STATUS
approved