21939427 has 4 divisors (see below), whose sum is σ = 21983040. Its totient is φ = 21895816.

The previous prime is 21939419. The next prime is 21939439. The reversal of 21939427 is 72493912.

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 21939427 - 2³ = 21939419 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21939527) 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, 21043 + ... + 22060.

It is an arithmetic number, because the mean of its divisors is an integer number (5495760).

Almost surely, 2^21939427 is an apocalyptic number.

21939427 is a deficient number, since it is larger than the sum of its proper divisors (43613).

21939427 is an equidigital number, since it uses as much as digits as its factorization.

21939427 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 43612.

The product of its digits is 27216, while the sum is 37.

The square root of 21939427 is about 4683.9542055831. The cubic root of 21939427 is about 279.9465331583.

It can be divided in two parts, 21939 and 427, that added together give a triangular number (22366 = T₂₁₁).

The spelling of 21939427 in words is "twenty-one million, nine hundred thirty-nine thousand, four hundred twenty-seven".