OFFSET
1,1
COMMENTS
If n is odd > 1 then the middle digit is ignored.
FORMULA
The left half of an n-digit number is the first floor(n/2) digits. The right half of an n-digit number is the last floor(n/2) digits.
EXAMPLE
20 is the first number with this property.
PROG
(PARI) leftprime(n) = { local(x, ln, y, lp, rp); for(x=1, n, y=Str(x); if(x > 9, ln=floor(length(y)/2), ln=1); lp = eval(left(y, ln)); rp = eval(right(y, ln)); if(isprime(lp)&& !isprime(rp), print1(x", ") ) ) }
CROSSREFS
KEYWORD
base,easy,nonn
AUTHOR
Cino Hilliard, Jan 29 2007
STATUS
approved