21801621 has 16 divisors (see below), whose sum is σ = 30369600. Its totient is φ = 13897728.

The previous prime is 21801617. The next prime is 21801641. The reversal of 21801621 is 12610812.

It is not a de Polignac number, because 21801621 - 2² = 21801617 is a prime.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21801601) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 4885 + ... + 8213.

It is an arithmetic number, because the mean of its divisors is an integer number (1898100).

Almost surely, 2^21801621 is an apocalyptic number.

It is an amenable number.

21801621 is a deficient number, since it is larger than the sum of its proper divisors (8567979).

21801621 is a wasteful number, since it uses less digits than its factorization.

21801621 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3428.

The product of its (nonzero) digits is 192, while the sum is 21.

The square root of 21801621 is about 4669.2205987723. The cubic root of 21801621 is about 279.3591679591.

It can be divided in two parts, 21801 and 621, that added together give a palindrome (22422).

The spelling of 21801621 in words is "twenty-one million, eight hundred one thousand, six hundred twenty-one".