21859812 has 54 divisors (see below), whose sum is σ = 59850882. Its totient is φ = 6724224.

The previous prime is 21859763. The next prime is 21859813. The reversal of 21859812 is 21895812.

It can be written as a sum of positive squares in 3 ways, for example, as 181476 + 21678336 = 426^2 + 4656^2 .

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21859813) 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 17 ways as a sum of consecutive naturals, for example, 4288 + ... + 7880.

Almost surely, 2^21859812 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 21859812, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29925441).

21859812 is an abundant number, since it is smaller than the sum of its proper divisors (37991070).

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

21859812 is a wasteful number, since it uses less digits than its factorization.

21859812 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3629 (or 3611 counting only the distinct ones).

The product of its digits is 11520, while the sum is 36.

The square root of 21859812 is about 4675.4477860415. The cubic root of 21859812 is about 279.6074942578.

The spelling of 21859812 in words is "twenty-one million, eight hundred fifty-nine thousand, eight hundred twelve".