21638918 has 16 divisors (see below), whose sum is σ = 37176864. Its totient is φ = 9253440.

The previous prime is 21638917. The next prime is 21638927. The reversal of 21638918 is 81983612.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21638917) 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 in 7 ways as a sum of consecutive naturals, for example, 6146 + ... + 9002.

It is an arithmetic number, because the mean of its divisors is an integer number (2323554).

Almost surely, 2^21638918 is an apocalyptic number.

21638918 is a deficient number, since it is larger than the sum of its proper divisors (15537946).

21638918 is a wasteful number, since it uses less digits than its factorization.

21638918 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3407.

The product of its digits is 20736, while the sum is 38.

The square root of 21638918 is about 4651.7650413580. The cubic root of 21638918 is about 278.6624901760.

The spelling of 21638918 in words is "twenty-one million, six hundred thirty-eight thousand, nine hundred eighteen".