OFFSET
1,5
COMMENTS
EXAMPLE
a(5) is the start of the counts for 2-digit primes. 11, 13 and 17 are the only 2-digit primes with leading digit 1 that remain prime read backward. It is not possible for a prime of more than 1 digit to lead with 2 and yield a prime read in reverse, so the following term, a(6), is the count for leading digit 3.
CROSSREFS
KEYWORD
nonn,base
AUTHOR
James G. Merickel, Dec 11 2012
STATUS
approved