The increasing sequence
1, 5, 6, 25, 26, 30, 31, 125, 126, … consists of all positive integers that can be formed by summing up distinct powers of 5 - from 1 to N presented in increasing order.
That is, 1 = 5^0, 5 = 5^1, 6 = 5^0 + 5^1, etc, etc.
What’s the 100th integer in this sequence?
we count to 100 in binary (1100100) for the 100th. Each digit is
0 or 1 times 5^n, where the digits go n=0,1,...
100th is 5^6 + 5^5 + 5^2 = 18775