21520217 has 4 divisors (see below), whose sum is σ = 22652880. Its totient is φ = 20387556.

The previous prime is 21520207. The next prime is 21520229. The reversal of 21520217 is 71202512.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21520217 - 2¹⁶ = 21454681 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21520207) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 566303 + ... + 566340.

It is an arithmetic number, because the mean of its divisors is an integer number (5663220).

Almost surely, 2^21520217 is an apocalyptic number.

It is an amenable number.

21520217 is a deficient number, since it is larger than the sum of its proper divisors (1132663).

21520217 is a wasteful number, since it uses less digits than its factorization.

21520217 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1132662.

The product of its (nonzero) digits is 280, while the sum is 20.

The square root of 21520217 is about 4638.9887906741. The cubic root of 21520217 is about 278.1520181975.

Adding to 21520217 its reverse (71202512), we get a palindrome (92722729).

The spelling of 21520217 in words is "twenty-one million, five hundred twenty thousand, two hundred seventeen".