The  rst 9 Demlo numbers have this property because the nth Demlo number is the square of the nth repunit.
The fraction of the numbers less than x with this property which are primeis on the order of ln ln ln x . Belphegor numbers are examples of this type of lnln xnumber which contain the string 666. Lychrel numbers are numbers which are not known to produce one of these numbers after repeated application of the reverse-then-add sequence; the smallest such number is 196. The  rst 9 Demlo numbers have this property because the nth Demlo number is the square of the nth repunit. All of these numbers with an even number of digits are divisible by   11. For ten points, identify this property held by numbers which are the same backwards as they are forwards.
The fraction of the numbers less than x with this property which are primeis on the order of ln ln ln x .
palindromes [accept word forms]