# Problem 486: Palindrome-containing strings

![graphic](img486.gif)

Let F5(n) be the number of strings s such that: s consists only of '0's
and '1's, s has length at most n, and s contains a palindromic substring
of length at least 5. For example, F5(4) = 0, F5(5) = 8, F5(6) = 42 and
F5(11) = 3844. Let D(L) be the number of integers n such that 5 ≤ n ≤ L
and F5(n) is divisible by 87654321. For example, D(107) = 0 and
D(5·109) = 51. Find D(1018).