21566542 has 4 divisors (see below), whose sum is σ = 32349816. Its totient is φ = 10783270.

The previous prime is 21566509. The next prime is 21566543. The reversal of 21566542 is 24566512.

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

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21566543) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5391634 + ... + 5391637.

It is an arithmetic number, because the mean of its divisors is an integer number (8087454).

Almost surely, 2^21566542 is an apocalyptic number.

21566542 is a deficient number, since it is larger than the sum of its proper divisors (10783274).

21566542 is a wasteful number, since it uses less digits than its factorization.

21566542 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10783273.

The product of its digits is 14400, while the sum is 31.

The square root of 21566542 is about 4643.9791127868. The cubic root of 21566542 is about 278.3514610047.

The spelling of 21566542 in words is "twenty-one million, five hundred sixty-six thousand, five hundred forty-two".