21779988 has 72 divisors (see below), whose sum is σ = 54999168. Its totient is φ = 6703488.

The previous prime is 21779987. The next prime is 21780001. The reversal of 21779988 is 88997712.

It is a self number, because there is not a number n which added to its sum of digits gives 21779988.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21779981) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 298320 + ... + 298392.

Almost surely, 2^21779988 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 21779988, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27499584).

21779988 is an abundant number, since it is smaller than the sum of its proper divisors (33219180).

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

21779988 is a wasteful number, since it uses less digits than its factorization.

21779988 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 173 (or 148 counting only the distinct ones).

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

The square root of 21779988 is about 4666.9034701823. The cubic root of 21779988 is about 279.2667378769.

The spelling of 21779988 in words is "twenty-one million, seven hundred seventy-nine thousand, nine hundred eighty-eight".