21138742 has 4 divisors (see below), whose sum is σ = 31708116. Its totient is φ = 10569370.

The previous prime is 21138737. The next prime is 21138751. The reversal of 21138742 is 24783112.

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

It is a self number, because there is not a number n which added to its sum of digits gives 21138742.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5284684 + ... + 5284687.

It is an arithmetic number, because the mean of its divisors is an integer number (7927029).

Almost surely, 2^21138742 is an apocalyptic number.

21138742 is a deficient number, since it is larger than the sum of its proper divisors (10569374).

21138742 is a wasteful number, since it uses less digits than its factorization.

21138742 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10569373.

The product of its digits is 2688, while the sum is 28.

The square root of 21138742 is about 4597.6887671960. The cubic root of 21138742 is about 276.4986696425.

The spelling of 21138742 in words is "twenty-one million, one hundred thirty-eight thousand, seven hundred forty-two".