21756139 has 4 divisors (see below), whose sum is σ = 22000680. Its totient is φ = 21511600.

The previous prime is 21756131. The next prime is 21756143. The reversal of 21756139 is 93165712.

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

It is a cyclic number.

It is not a de Polignac number, because 21756139 - 2³ = 21756131 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21756131) 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, 122137 + ... + 122314.

It is an arithmetic number, because the mean of its divisors is an integer number (5500170).

Almost surely, 2^21756139 is an apocalyptic number.

21756139 is a deficient number, since it is larger than the sum of its proper divisors (244541).

21756139 is an equidigital number, since it uses as much as digits as its factorization.

21756139 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 244540.

The product of its digits is 11340, while the sum is 34.

The square root of 21756139 is about 4664.3476499935. The cubic root of 21756139 is about 279.1647686611.

The spelling of 21756139 in words is "twenty-one million, seven hundred fifty-six thousand, one hundred thirty-nine".