21978015 has 16 divisors (see below), whose sum is σ = 35229696. Its totient is φ = 11700000.

The previous prime is 21978007. The next prime is 21978017. The reversal of 21978015 is 51087912.

It is not a de Polignac number, because 21978015 - 2³ = 21978007 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21978017) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 10290 + ... + 12240.

It is an arithmetic number, because the mean of its divisors is an integer number (2201856).

Almost surely, 2^21978015 is an apocalyptic number.

21978015 is a deficient number, since it is larger than the sum of its proper divisors (13251681).

21978015 is a wasteful number, since it uses less digits than its factorization.

21978015 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2710.

The product of its (nonzero) digits is 5040, while the sum is 33.

The square root of 21978015 is about 4688.0715651534. The cubic root of 21978015 is about 280.1105643286.

The spelling of 21978015 in words is "twenty-one million, nine hundred seventy-eight thousand, fifteen".