21879990 has 128 divisors (see below), whose sum is σ = 65318400. Its totient is φ = 5166720.

The previous prime is 21879961. The next prime is 21880009. The reversal of 21879990 is 9997812.

It is a Harshad number since it is a multiple of its sum of digits (45).

It is a Curzon number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 157341 + ... + 157479.

It is an arithmetic number, because the mean of its divisors is an integer number (510300).

Almost surely, 2^21879990 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21879990, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32659200).

21879990 is an abundant number, since it is smaller than the sum of its proper divisors (43438410).

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

21879990 is a wasteful number, since it uses less digits than its factorization.

21879990 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 219 (or 213 counting only the distinct ones).

The product of its (nonzero) digits is 81648, while the sum is 45.

The square root of 21879990 is about 4677.6051564877. The cubic root of 21879990 is about 279.6934996476.

It can be divided in two parts, 218 and 79990, that added together give a palindrome (80208).

The spelling of 21879990 in words is "twenty-one million, eight hundred seventy-nine thousand, nine hundred ninety".