21157637 has 4 divisors (see below), whose sum is σ = 21166860. Its totient is φ = 21148416.

The previous prime is 21157627. The next prime is 21157649. The reversal of 21157637 is 73675112.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 14182756 + 6974881 = 3766^2 + 2641^2 .

It is a cyclic number.

It is not a de Polignac number, because 21157637 - 2⁶ = 21157573 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21157627) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1823 + ... + 6755.

It is an arithmetic number, because the mean of its divisors is an integer number (5291715).

Almost surely, 2^21157637 is an apocalyptic number.

It is an amenable number.

21157637 is a deficient number, since it is larger than the sum of its proper divisors (9223).

21157637 is an equidigital number, since it uses as much as digits as its factorization.

21157637 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9222.

The product of its digits is 8820, while the sum is 32.

The square root of 21157637 is about 4599.7431450028. The cubic root of 21157637 is about 276.5810284776.

The spelling of 21157637 in words is "twenty-one million, one hundred fifty-seven thousand, six hundred thirty-seven".