OFFSET
1,1
COMMENTS
Start with p=prime(n). If concat(p,3) is prime, then this is a(n), else consider concat(p,p,3), and so on.
EXAMPLE
For a(1), start with prime(1)=2. Since appending a digit 3 yields the prime 23, a(1)=23.
For a(2), start with prime(2)=3. Since concatenating any number of digits '3' never yields a prime, a(2)=0.
For a(6), starting with prime(6)=13, one has to take 5 concatenations of itself before a prime is obtained when a final digit '3' is appended, thus a(6)=13131313133.
a(22)=0 since the concatenation of prime(22)=79 with itself, followed by a 3, is always composite. - Giovanni Resta, Apr 07 2006
CROSSREFS
KEYWORD
base,nonn
AUTHOR
Amarnath Murthy, Mar 28 2004
EXTENSIONS
a(15)-a(21) from Stefan Steinerberger, Nov 09 2005
More terms from Giovanni Resta, Apr 07 2006
STATUS
approved