20216521 has 4 divisors (see below), whose sum is σ = 21771652. Its totient is φ = 18661392.

The previous prime is 20216507. The next prime is 20216569. The reversal of 20216521 is 12561202.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 12561202 = 2 ⋅6280601.

It can be written as a sum of positive squares in 2 ways, for example, as 13220496 + 6996025 = 3636^2 + 2645^2 .

It is a cyclic number.

It is not a de Polignac number, because 20216521 - 2⁵ = 20216489 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20216501) 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, 777546 + ... + 777571.

It is an arithmetic number, because the mean of its divisors is an integer number (5442913).

Almost surely, 2^20216521 is an apocalyptic number.

It is an amenable number.

20216521 is a deficient number, since it is larger than the sum of its proper divisors (1555131).

20216521 is a wasteful number, since it uses less digits than its factorization.

20216521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1555130.

The product of its (nonzero) digits is 240, while the sum is 19.

The square root of 20216521 is about 4496.2785723307. The cubic root of 20216521 is about 272.4177952527.

Adding to 20216521 its reverse (12561202), we get a palindrome (32777723).

The spelling of 20216521 in words is "twenty million, two hundred sixteen thousand, five hundred twenty-one".