21979788 has 24 divisors (see below), whose sum is σ = 51787008. Its totient is φ = 7255056.

The previous prime is 21979787. The next prime is 21979807. The reversal of 21979788 is 88797912.

It is a super-2 number, since 2×21979788² = 966222161049888, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 21979788.

It is not an unprimeable number, because it can be changed into a prime (21979781) 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, 7656 + ... + 10127.

It is an arithmetic number, because the mean of its divisors is an integer number (2157792).

Almost surely, 2^21979788 is an apocalyptic number.

It is an amenable number.

21979788 is an abundant number, since it is smaller than the sum of its proper divisors (29807220).

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

21979788 is a wasteful number, since it uses less digits than its factorization.

21979788 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 17893 (or 17891 counting only the distinct ones).

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

The square root of 21979788 is about 4688.2606582826. The cubic root of 21979788 is about 280.1180964416.

The spelling of 21979788 in words is "twenty-one million, nine hundred seventy-nine thousand, seven hundred eighty-eight".