21981318 has 16 divisors (see below), whose sum is σ = 44159040. Its totient is φ = 7294376.

The previous prime is 21981313. The next prime is 21981319. The reversal of 21981318 is 81318912.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21981313) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 6708 + ... + 9431.

It is an arithmetic number, because the mean of its divisors is an integer number (2759940).

Almost surely, 2^21981318 is an apocalyptic number.

21981318 is an abundant number, since it is smaller than the sum of its proper divisors (22177722).

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

21981318 is a wasteful number, since it uses less digits than its factorization.

21981318 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16371.

The product of its digits is 3456, while the sum is 33.

The square root of 21981318 is about 4688.4238289643. The cubic root of 21981318 is about 280.1245959090.

The spelling of 21981318 in words is "twenty-one million, nine hundred eighty-one thousand, three hundred eighteen".