21801657 has 4 divisors (see below), whose sum is σ = 29068880. Its totient is φ = 14534436.

The previous prime is 21801653. The next prime is 21801673. The reversal of 21801657 is 75610812.

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 not a de Polignac number, because 21801657 - 2² = 21801653 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21801653) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3633607 + ... + 3633612.

It is an arithmetic number, because the mean of its divisors is an integer number (7267220).

Almost surely, 2^21801657 is an apocalyptic number.

It is an amenable number.

21801657 is a deficient number, since it is larger than the sum of its proper divisors (7267223).

21801657 is an equidigital number, since it uses as much as digits as its factorization.

21801657 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7267222.

The product of its (nonzero) digits is 3360, while the sum is 30.

The square root of 21801657 is about 4669.2244538039. The cubic root of 21801657 is about 279.3593217233.

The spelling of 21801657 in words is "twenty-one million, eight hundred one thousand, six hundred fifty-seven".