21997878 has 16 divisors (see below), whose sum is σ = 50280960. Its totient is φ = 6285096.

The previous prime is 21997861. The next prime is 21997931. The reversal of 21997878 is 87879912.

It is a self number, because there is not a number n which added to its sum of digits gives 21997878.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 261838 + ... + 261921.

It is an arithmetic number, because the mean of its divisors is an integer number (3142560).

Almost surely, 2^21997878 is an apocalyptic number.

21997878 is an abundant number, since it is smaller than the sum of its proper divisors (28283082).

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

21997878 is a wasteful number, since it uses less digits than its factorization.

21997878 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 523771.

The product of its digits is 508032, while the sum is 51.

The square root of 21997878 is about 4690.1895484085. The cubic root of 21997878 is about 280.1949237949.

The spelling of 21997878 in words is "twenty-one million, nine hundred ninety-seven thousand, eight hundred seventy-eight".