21663021 has 16 divisors (see below), whose sum is σ = 30513600. Its totient is φ = 13632768.

The previous prime is 21662989. The next prime is 21663041. The reversal of 21663021 is 12036612.

It is a happy number.

It is not a de Polignac number, because 21663021 - 2⁵ = 21662989 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21663041) 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, 21685 + ... + 22661.

It is an arithmetic number, because the mean of its divisors is an integer number (1907100).

Almost surely, 2^21663021 is an apocalyptic number.

It is an amenable number.

21663021 is a deficient number, since it is larger than the sum of its proper divisors (8850579).

21663021 is a wasteful number, since it uses less digits than its factorization.

21663021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1388.

The product of its (nonzero) digits is 432, while the sum is 21.

The square root of 21663021 is about 4654.3550573629. The cubic root of 21663021 is about 278.7659166309.

Adding to 21663021 its reverse (12036612), we get a palindrome (33699633).

The spelling of 21663021 in words is "twenty-one million, six hundred sixty-three thousand, twenty-one".