21137921 has 12 divisors (see below), whose sum is σ = 24700608. Its totient is φ = 17719752.

The previous prime is 21137917. The next prime is 21137923. The reversal of 21137921 is 12973112.

It is not a de Polignac number, because 21137921 - 2² = 21137917 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21137923) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 14780 + ... + 16146.

It is an arithmetic number, because the mean of its divisors is an integer number (2058384).

Almost surely, 2^21137921 is an apocalyptic number.

It is an amenable number.

21137921 is a deficient number, since it is larger than the sum of its proper divisors (3562687).

21137921 is an equidigital number, since it uses as much as digits as its factorization.

21137921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1468 (or 1421 counting only the distinct ones).

The product of its digits is 756, while the sum is 26.

The square root of 21137921 is about 4597.5994823386. The cubic root of 21137921 is about 276.4950899854.

The spelling of 21137921 in words is "twenty-one million, one hundred thirty-seven thousand, nine hundred twenty-one".