21549918 has 32 divisors (see below), whose sum is σ = 46712736. Its totient is φ = 6588288.

The previous prime is 21549911. The next prime is 21549949. The reversal of 21549918 is 81994512.

It is a Harshad number since it is a multiple of its sum of digits (39).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21549911) 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 in 15 ways as a sum of consecutive naturals, for example, 12696 + ... + 14292.

It is an arithmetic number, because the mean of its divisors is an integer number (1459773).

Almost surely, 2^21549918 is an apocalyptic number.

21549918 is an abundant number, since it is smaller than the sum of its proper divisors (25162818).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21549918 is a wasteful number, since it uses less digits than its factorization.

21549918 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1788.

The product of its digits is 25920, while the sum is 39.

The square root of 21549918 is about 4642.1889233421. The cubic root of 21549918 is about 278.2799226601.

The spelling of 21549918 in words is "twenty-one million, five hundred forty-nine thousand, nine hundred eighteen".