21979216 has 80 divisors (see below), whose sum is σ = 51603840. Its totient is φ = 8870400.

The previous prime is 21979213. The next prime is 21979229. The reversal of 21979216 is 61297912.

21979216 = 459² + 460² + ... + 545².

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21979213) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 217566 + ... + 217666.

It is an arithmetic number, because the mean of its divisors is an integer number (645048).

Almost surely, 2^21979216 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21979216, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25801920).

21979216 is an abundant number, since it is smaller than the sum of its proper divisors (29624624).

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

21979216 is a wasteful number, since it uses less digits than its factorization.

21979216 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 212 (or 206 counting only the distinct ones).

The product of its digits is 13608, while the sum is 37.

The square root of 21979216 is about 4688.1996544516. The cubic root of 21979216 is about 280.1156664979.

The spelling of 21979216 in words is "twenty-one million, nine hundred seventy-nine thousand, two hundred sixteen".