21979191 has 32 divisors (see below), whose sum is σ = 33384960. Its totient is φ = 12760704.

The previous prime is 21979189. The next prime is 21979213. The reversal of 21979191 is 19197912.

It is not a de Polignac number, because 21979191 - 2¹ = 21979189 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (39).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21979121) by changing a digit.

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 31 ways as a sum of consecutive naturals, for example, 95865 + ... + 96093.

It is an arithmetic number, because the mean of its divisors is an integer number (1043280).

Almost surely, 2^21979191 is an apocalyptic number.

21979191 is a deficient number, since it is larger than the sum of its proper divisors (11405769).

21979191 is a wasteful number, since it uses less digits than its factorization.

21979191 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 375.

The product of its digits is 10206, while the sum is 39.

The square root of 21979191 is about 4688.1969881821. The cubic root of 21979191 is about 280.1155602931.

The spelling of 21979191 in words is "twenty-one million, nine hundred seventy-nine thousand, one hundred ninety-one".