20721189 has 4 divisors (see below), whose sum is σ = 27628256. Its totient is φ = 13814124.

The previous prime is 20721163. The next prime is 20721209. The reversal of 20721189 is 98112702.

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 not a de Polignac number, because 20721189 - 2¹² = 20717093 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20721089) 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, 3453529 + ... + 3453534.

It is an arithmetic number, because the mean of its divisors is an integer number (6907064).

Almost surely, 2^20721189 is an apocalyptic number.

It is an amenable number.

20721189 is a deficient number, since it is larger than the sum of its proper divisors (6907067).

20721189 is an equidigital number, since it uses as much as digits as its factorization.

20721189 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6907066.

The product of its (nonzero) digits is 2016, while the sum is 30.

The square root of 20721189 is about 4552.0532729747. The cubic root of 20721189 is about 274.6659922835.

It can be divided in two parts, 20721 and 189, that added together give a triangular number (20910 = T₂₀₄).

The spelling of 20721189 in words is "twenty million, seven hundred twenty-one thousand, one hundred eighty-nine".