21789990 has 48 divisors (see below), whose sum is σ = 57356208. Its totient is φ = 5738688.

The previous prime is 21789967. The next prime is 21789997. The reversal of 21789990 is 9998712.

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 not an unprimeable number, because it can be changed into a prime (21789997) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 6012 + ... + 8928.

It is an arithmetic number, because the mean of its divisors is an integer number (1194921).

Almost surely, 2^21789990 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21789990, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28678104).

21789990 is an abundant number, since it is smaller than the sum of its proper divisors (35566218).

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

21789990 is a wasteful number, since it uses less digits than its factorization.

21789990 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3013 (or 3010 counting only the distinct ones).

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

The square root of 21789990 is about 4667.9749356654. The cubic root of 21789990 is about 279.3094804539.

The spelling of 21789990 in words is "twenty-one million, seven hundred eighty-nine thousand, nine hundred ninety".