21979997 has 16 divisors (see below), whose sum is σ = 25224192. Its totient is φ = 18973440.

The previous prime is 21979957. The next prime is 21980003. The reversal of 21979997 is 79997912.

It is a cyclic number.

It is not a de Polignac number, because 21979997 - 2²⁴ = 5202781 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21979907) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 59708 + ... + 60074.

It is an arithmetic number, because the mean of its divisors is an integer number (1576512).

Almost surely, 2^21979997 is an apocalyptic number.

It is an amenable number.

21979997 is a deficient number, since it is larger than the sum of its proper divisors (3244195).

21979997 is a wasteful number, since it uses less digits than its factorization.

21979997 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 668.

The product of its digits is 642978, while the sum is 53.

The square root of 21979997 is about 4688.2829479459. The cubic root of 21979997 is about 280.1189842951.

The spelling of 21979997 in words is "twenty-one million, nine hundred seventy-nine thousand, nine hundred ninety-seven".