21091807 has 8 divisors (see below), whose sum is σ = 23063040. Its totient is φ = 19129560.

The previous prime is 21091793. The next prime is 21091823. The reversal of 21091807 is 70819012.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21091807 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21091867) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 3268 + ... + 7270.

It is an arithmetic number, because the mean of its divisors is an integer number (2882880).

Almost surely, 2^21091807 is an apocalyptic number.

21091807 is a deficient number, since it is larger than the sum of its proper divisors (1971233).

21091807 is a wasteful number, since it uses less digits than its factorization.

21091807 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4493.

The product of its (nonzero) digits is 1008, while the sum is 28.

The square root of 21091807 is about 4592.5817357996. The cubic root of 21091807 is about 276.2938784952.

It can be divided in two parts, 2109 and 1807, that added together give a triangular number (3916 = T₈₈).

The spelling of 21091807 in words is "twenty-one million, ninety-one thousand, eight hundred seven".