21644542 has 4 divisors (see below), whose sum is σ = 32466816. Its totient is φ = 10822270.

The previous prime is 21644531. The next prime is 21644543. The reversal of 21644542 is 24544612.

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 21644542.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21644543) 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 as a sum of consecutive naturals, namely, 5411134 + ... + 5411137.

It is an arithmetic number, because the mean of its divisors is an integer number (8116704).

Almost surely, 2^21644542 is an apocalyptic number.

21644542 is a deficient number, since it is larger than the sum of its proper divisors (10822274).

21644542 is a wasteful number, since it uses less digits than its factorization.

21644542 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10822273.

The product of its digits is 7680, while the sum is 28.

The square root of 21644542 is about 4652.3695038120. The cubic root of 21644542 is about 278.6866297393.

The spelling of 21644542 in words is "twenty-one million, six hundred forty-four thousand, five hundred forty-two".