21390742 has 4 divisors (see below), whose sum is σ = 32086116. Its totient is φ = 10695370.

The previous prime is 21390727. The next prime is 21390767. The reversal of 21390742 is 24709312.

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 21390742.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5347684 + ... + 5347687.

It is an arithmetic number, because the mean of its divisors is an integer number (8021529).

Almost surely, 2^21390742 is an apocalyptic number.

21390742 is a deficient number, since it is larger than the sum of its proper divisors (10695374).

21390742 is a wasteful number, since it uses less digits than its factorization.

21390742 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10695373.

The product of its (nonzero) digits is 3024, while the sum is 28.

The square root of 21390742 is about 4625.0126486314. The cubic root of 21390742 is about 277.5930678285.

The spelling of 21390742 in words is "twenty-one million, three hundred ninety thousand, seven hundred forty-two".