20819621 has 4 divisors (see below), whose sum is σ = 20959500. Its totient is φ = 20679744.

The previous prime is 20819563. The next prime is 20819629. The reversal of 20819621 is 12691802.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 2070721 + 18748900 = 1439^2 + 4330^2 .

It is a cyclic number.

It is not a de Polignac number, because 20819621 - 2¹⁰ = 20818597 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20819629) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 69716 + ... + 70013.

It is an arithmetic number, because the mean of its divisors is an integer number (5239875).

Almost surely, 2^20819621 is an apocalyptic number.

It is an amenable number.

20819621 is a deficient number, since it is larger than the sum of its proper divisors (139879).

20819621 is a wasteful number, since it uses less digits than its factorization.

20819621 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 139878.

The product of its (nonzero) digits is 1728, while the sum is 29.

The square root of 20819621 is about 4562.8522877691. The cubic root of 20819621 is about 275.1002213220.

The spelling of 20819621 in words is "twenty million, eight hundred nineteen thousand, six hundred twenty-one".