21500421 has 8 divisors (see below), whose sum is σ = 28705824. Its totient is φ = 14314320.

The previous prime is 21500321. The next prime is 21500429. The reversal of 21500421 is 12400512.

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

It is not a de Polignac number, because 21500421 - 2¹⁵ = 21467653 is a prime.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21500421.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21500429) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1986 + ... + 6851.

It is an arithmetic number, because the mean of its divisors is an integer number (3588228).

Almost surely, 2^21500421 is an apocalyptic number.

It is an amenable number.

21500421 is a deficient number, since it is larger than the sum of its proper divisors (7205403).

21500421 is an equidigital number, since it uses as much as digits as its factorization.

21500421 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9651.

The product of its (nonzero) digits is 80, while the sum is 15.

The square root of 21500421 is about 4636.8546451231. The cubic root of 21500421 is about 278.0667032804.

Adding to 21500421 its reverse (12400512), we get a palindrome (33900933).

Subtracting from 21500421 its reverse (12400512), we obtain a palindrome (9099909).

The spelling of 21500421 in words is "twenty-one million, five hundred thousand, four hundred twenty-one".