21856860 has 72 divisors (see below), whose sum is σ = 68455296. Its totient is φ = 5639040.

The previous prime is 21856847. The next prime is 21856867. The reversal of 21856860 is 6865812.

It is a happy number.

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 (21856867) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 3622 + ... + 7538.

It is an arithmetic number, because the mean of its divisors is an integer number (950768).

Almost surely, 2^21856860 is an apocalyptic number.

21856860 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21856860, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (34227648).

21856860 is an abundant number, since it is smaller than the sum of its proper divisors (46598436).

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

21856860 is a wasteful number, since it uses less digits than its factorization.

21856860 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3963 (or 3958 counting only the distinct ones).

The product of its (nonzero) digits is 23040, while the sum is 36.

The square root of 21856860 is about 4675.1320836956. The cubic root of 21856860 is about 279.5949074085.

It can be divided in two parts, 2185 and 6860, that added together give a triangular number (9045 = T₁₃₄).

The spelling of 21856860 in words is "twenty-one million, eight hundred fifty-six thousand, eight hundred sixty".