Nearly prime number is an integer positive number for which it is possible to find such primes P1 and P2 that given number is equal to P1*P2. There is given a s...

Once upon a time Professor Idioticideasinventor was travelling by train. Watching cheerless landscape outside the window, he decided to invent the theme of his ...

A frog is crossing a river. The river is divided into x units and at each unit there may or may not exist a stone. The frog can jump on a stone, but it must not...

For given integer N (1<=N<=10^4) find amount of positive numbers not greater than N that coprime with N. Let us call two positive integers (say, A and B, for ex...

Given a positive integer n and you can do operations as follow:

Find the nth digit of the infinite integer sequence 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, …

Given an integer n, return 1 - n in lexicographical order.

A character in UTF8 can be from 1 to 4 bytes long, subjected to the following rules:

Given an integer array with all positive numbers and no duplicates, find the number of possible combinations that add up to a positive integer target.

Let f(n) be a sum of digits for positive integer n. If f(n) is one-digit number then it is a digital root for n and otherwise digital root of n is equal to digi...