puzzles
For a particular value of x, write the sequence of numbers 1,2,3,…,x. Now count the number of times you had to write the digit ‘1’ in that sequence and let f(x) be this count. To give you some examples:
f(1)=1 (1)
f(2)=1 (1,2)
f(3)=1 (1,2,3)
f(10)=2 (1,2,3,4,5,6,7,8,9,10)
f(11)=4 (1,2,3,4,5,6,7,8,9,10,11)
Right, so f(1)=1. What is the next x such that f(x)=x?