21971818 has 16 divisors (see below), whose sum is σ = 36832320. Its totient is φ = 9743200.

The previous prime is 21971801. The next prime is 21971827. The reversal of 21971818 is 81817912.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 11278 + ... + 13081.

It is an arithmetic number, because the mean of its divisors is an integer number (2302020).

Almost surely, 2^21971818 is an apocalyptic number.

21971818 is a deficient number, since it is larger than the sum of its proper divisors (14860502).

21971818 is a wasteful number, since it uses less digits than its factorization.

21971818 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 24413.

The product of its digits is 8064, while the sum is 37.

The square root of 21971818 is about 4687.4105858139. The cubic root of 21971818 is about 280.0842348604.

The spelling of 21971818 in words is "twenty-one million, nine hundred seventy-one thousand, eight hundred eighteen".