21637979 has 12 divisors (see below), whose sum is σ = 24917400. Its totient is φ = 18632160.

The previous prime is 21637961. The next prime is 21637997. The reversal of 21637979 is 97973612.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (21637961) and next prime (21637997).

It is not a de Polignac number, because 21637979 - 2¹² = 21633883 is a prime.

It is a Smith number, since the sum of its digits (44) coincides with the sum of the digits of its prime factors.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21637909) 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 11 ways as a sum of consecutive naturals, for example, 1247 + ... + 6695.

It is an arithmetic number, because the mean of its divisors is an integer number (2076450).

Almost surely, 2^21637979 is an apocalyptic number.

21637979 is a deficient number, since it is larger than the sum of its proper divisors (3279421).

21637979 is a wasteful number, since it uses less digits than its factorization.

21637979 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5498 (or 5479 counting only the distinct ones).

The product of its digits is 142884, while the sum is 44.

The square root of 21637979 is about 4651.6641108317. The cubic root of 21637979 is about 278.6584593542.

The spelling of 21637979 in words is "twenty-one million, six hundred thirty-seven thousand, nine hundred seventy-nine".