21639181 has 4 divisors (see below), whose sum is σ = 22912092. Its totient is φ = 20366272.

The previous prime is 21639151. The next prime is 21639199. The reversal of 21639181 is 18193612.

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 8462281 + 13176900 = 2909^2 + 3630^2 .

It is not a de Polignac number, because 21639181 - 2⁷ = 21639053 is a prime.

It is a super-2 number, since 2×21639181² = 936508308701522, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21639151) 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, 636430 + ... + 636463.

It is an arithmetic number, because the mean of its divisors is an integer number (5728023).

Almost surely, 2^21639181 is an apocalyptic number.

It is an amenable number.

21639181 is a deficient number, since it is larger than the sum of its proper divisors (1272911).

21639181 is a wasteful number, since it uses less digits than its factorization.

21639181 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1272910.

The product of its digits is 2592, while the sum is 31.

The square root of 21639181 is about 4651.7933101117. The cubic root of 21639181 is about 278.6636191286.

The spelling of 21639181 in words is "twenty-one million, six hundred thirty-nine thousand, one hundred eighty-one".