21391042 has 8 divisors (see below), whose sum is σ = 32115132. Its totient is φ = 10686000.

The previous prime is 21391033. The next prime is 21391057. The reversal of 21391042 is 24019312.

It can be written as a sum of positive squares in 2 ways, for example, as 21169201 + 221841 = 4601^2 + 471^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

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 in 3 ways as a sum of consecutive naturals, for example, 1509 + ... + 6712.

Almost surely, 2^21391042 is an apocalyptic number.

21391042 is a deficient number, since it is larger than the sum of its proper divisors (10724090).

21391042 is a wasteful number, since it uses less digits than its factorization.

21391042 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9524.

The product of its (nonzero) digits is 432, while the sum is 22.

The square root of 21391042 is about 4625.0450808614. The cubic root of 21391042 is about 277.5943655477.

The spelling of 21391042 in words is "twenty-one million, three hundred ninety-one thousand, forty-two".