21636021 has 8 divisors (see below), whose sum is σ = 31470624. Its totient is φ = 13112720.

The previous prime is 21636007. The next prime is 21636023. The reversal of 21636021 is 12063612.

It is a happy number.

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

It is a cyclic number.

It is not a de Polignac number, because 21636021 - 2¹¹ = 21633973 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 (21636023) 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, 327786 + ... + 327851.

It is an arithmetic number, because the mean of its divisors is an integer number (3933828).

Almost surely, 2^21636021 is an apocalyptic number.

It is an amenable number.

21636021 is a deficient number, since it is larger than the sum of its proper divisors (9834603).

21636021 is a wasteful number, since it uses less digits than its factorization.

21636021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 655651.

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

The square root of 21636021 is about 4651.4536437548. The cubic root of 21636021 is about 278.6500539216.

Adding to 21636021 its reverse (12063612), we get a palindrome (33699633).

The spelling of 21636021 in words is "twenty-one million, six hundred thirty-six thousand, twenty-one".