21908749 has 4 divisors (see below), whose sum is σ = 21966336. Its totient is φ = 21851164.

The previous prime is 21908743. The next prime is 21908753. The reversal of 21908749 is 94780912.

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 not a de Polignac number, because 21908749 - 2¹⁵ = 21875981 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 (21908743) 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, 28219 + ... + 28984.

It is an arithmetic number, because the mean of its divisors is an integer number (5491584).

Almost surely, 2^21908749 is an apocalyptic number.

It is an amenable number.

21908749 is a deficient number, since it is larger than the sum of its proper divisors (57587).

21908749 is an equidigital number, since it uses as much as digits as its factorization.

21908749 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 57586.

The product of its (nonzero) digits is 36288, while the sum is 40.

The square root of 21908749 is about 4680.6782628162. The cubic root of 21908749 is about 279.8159887914.

The spelling of 21908749 in words is "twenty-one million, nine hundred eight thousand, seven hundred forty-nine".