OFFSET
1,1
COMMENTS
Demanding that the index is not a prime would lead to A155025 instead.
EXAMPLE
For the index n=3, a prime, p = prime(3)=5, the concatenation 35 is composite, so p=5 is added to the sequence.
For the index n=5, a prime, p = prime(5)=11, the concatenation 511 is composite, so p=11 is added to the sequence.
For the index n=6, not a prime, nothing is added to the sequence.
For the index n=7, a prime, p = prime(7)=17, the concatenation 717 is composite, so p=17 is added to the sequence.
MATHEMATICA
Prime[#]&/@Select[Prime[Range[70]], CompositeQ[FromDigits[Join[ IntegerDigits[ #], IntegerDigits[ Prime[#]]]]]&] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Jun 14 2019 *)
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Juri-Stepan Gerasimov, Jan 19 2009
EXTENSIONS
Definition clarified, sequence extended by R. J. Mathar, Oct 14 2009
STATUS
approved