21316637 has 4 divisors (see below), whose sum is σ = 21359520. Its totient is φ = 21273756.

The previous prime is 21316619. The next prime is 21316639. The reversal of 21316637 is 73661312.

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.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21316637 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 (21316639) 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, 20687 + ... + 21692.

It is an arithmetic number, because the mean of its divisors is an integer number (5339880).

Almost surely, 2^21316637 is an apocalyptic number.

It is an amenable number.

21316637 is a deficient number, since it is larger than the sum of its proper divisors (42883).

21316637 is an equidigital number, since it uses as much as digits as its factorization.

21316637 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 42882.

The product of its digits is 4536, while the sum is 29.

The square root of 21316637 is about 4616.9943686342. The cubic root of 21316637 is about 277.2721371629.

Adding to 21316637 its reverse (73661312), we get a palindrome (94977949).

The spelling of 21316637 in words is "twenty-one million, three hundred sixteen thousand, six hundred thirty-seven".