21013637 has 4 divisors (see below), whose sum is σ = 21023040. Its totient is φ = 21004236.

The previous prime is 21013633. The next prime is 21013709. The reversal of 21013637 is 73631012.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 21013637 - 2² = 21013633 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 (21013631) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 788 + ... + 6530.

It is an arithmetic number, because the mean of its divisors is an integer number (5255760).

Almost surely, 2^21013637 is an apocalyptic number.

It is an amenable number.

21013637 is a deficient number, since it is larger than the sum of its proper divisors (9403).

21013637 is an equidigital number, since it uses as much as digits as its factorization.

21013637 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9402.

The product of its (nonzero) digits is 756, while the sum is 23.

The square root of 21013637 is about 4584.0633721623. The cubic root of 21013637 is about 275.9521244761.

Adding to 21013637 its reverse (73631012), we get a palindrome (94644649).

The spelling of 21013637 in words is "twenty-one million, thirteen thousand, six hundred thirty-seven".