21638291 has 4 divisors (see below), whose sum is σ = 21665784. Its totient is φ = 21610800.

The previous prime is 21638273. The next prime is 21638311. The reversal of 21638291 is 19283612.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21638291 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21638231) 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, 12530 + ... + 14151.

It is an arithmetic number, because the mean of its divisors is an integer number (5416446).

Almost surely, 2^21638291 is an apocalyptic number.

21638291 is a deficient number, since it is larger than the sum of its proper divisors (27493).

21638291 is an equidigital number, since it uses as much as digits as its factorization.

21638291 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 27492.

The product of its digits is 5184, while the sum is 32.

The square root of 21638291 is about 4651.6976470962. The cubic root of 21638291 is about 278.6597986817.

The spelling of 21638291 in words is "twenty-one million, six hundred thirty-eight thousand, two hundred ninety-one".