21520221 has 8 divisors (see below), whose sum is σ = 28718400. Its totient is φ = 14334432.

The previous prime is 21520207. The next prime is 21520229. The reversal of 21520221 is 12202512.

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

It is not a de Polignac number, because 21520221 - 2⁵ = 21520189 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21520221.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21520229) 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, 2305 + ... + 6953.

It is an arithmetic number, because the mean of its divisors is an integer number (3589800).

Almost surely, 2^21520221 is an apocalyptic number.

It is an amenable number.

21520221 is a deficient number, since it is larger than the sum of its proper divisors (7198179).

21520221 is a wasteful number, since it uses less digits than its factorization.

21520221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6195.

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

The square root of 21520221 is about 4638.9892218025. The cubic root of 21520221 is about 278.1520354311.

Adding to 21520221 its reverse (12202512), we get a palindrome (33722733).

The spelling of 21520221 in words is "twenty-one million, five hundred twenty thousand, two hundred twenty-one".