21638534 has 4 divisors (see below), whose sum is σ = 32457804. Its totient is φ = 10819266.

The previous prime is 21638531. The next prime is 21638567. The reversal of 21638534 is 43583612.

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 21638534.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21638531) by changing a digit.

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, 5409632 + ... + 5409635.

It is an arithmetic number, because the mean of its divisors is an integer number (8114451).

Almost surely, 2^21638534 is an apocalyptic number.

21638534 is a deficient number, since it is larger than the sum of its proper divisors (10819270).

21638534 is a wasteful number, since it uses less digits than its factorization.

21638534 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10819269.

The product of its digits is 17280, while the sum is 32.

The square root of 21638534 is about 4651.7237665192. The cubic root of 21638534 is about 278.6608418029.

The spelling of 21638534 in words is "twenty-one million, six hundred thirty-eight thousand, five hundred thirty-four".