21978915 has 64 divisors (see below), whose sum is σ = 44236800. Its totient is φ = 9085824.

The previous prime is 21978899. The next prime is 21978917. The reversal of 21978915 is 51987912.

It is not a de Polignac number, because 21978915 - 2⁴ = 21978899 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21978917) by changing a digit.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 45646 + ... + 46124.

It is an arithmetic number, because the mean of its divisors is an integer number (691200).

Almost surely, 2^21978915 is an apocalyptic number.

21978915 is an abundant number, since it is smaller than the sum of its proper divisors (22257885).

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

21978915 is a wasteful number, since it uses less digits than its factorization.

21978915 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 536.

The product of its digits is 45360, while the sum is 42.

The square root of 21978915 is about 4688.1675524665. The cubic root of 21978915 is about 280.1143877869.

The spelling of 21978915 in words is "twenty-one million, nine hundred seventy-eight thousand, nine hundred fifteen".