# Problem 529: 10-substrings
A 10-substring of a number is a substring of its digits that sum to 10.
For example, the 10-substrings of the number 3523014 are: 3523014
3523014 3523014 3523014A number is called 10-substring-friendly if every
one of its digits belongs to a 10-substring. For example, 3523014 is
10-substring-friendly, but 28546 is not. Let T(n) be the number of
10-substring-friendly numbers from 1 to 10n (inclusive). For example
T(2) = 9 and T(5) = 3492. Find T(1018) mod 1 000 000 007.