21866520 has 128 divisors (see below), whose sum is σ = 71850240. Its totient is φ = 5291520.

The previous prime is 21866483. The next prime is 21866527. The reversal of 21866520 is 2566812.

It is a Harshad number since it is a multiple of its sum of digits (30).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21866527) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 166855 + ... + 166985.

It is an arithmetic number, because the mean of its divisors is an integer number (561330).

Almost surely, 2^21866520 is an apocalyptic number.

21866520 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 21866520, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (35925120).

21866520 is an abundant number, since it is smaller than the sum of its proper divisors (49983720).

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

21866520 is a wasteful number, since it uses less digits than its factorization.

21866520 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 265 (or 261 counting only the distinct ones).

The product of its (nonzero) digits is 5760, while the sum is 30.

The square root of 21866520 is about 4676.1650954602. The cubic root of 21866520 is about 279.6360918696.

The spelling of 21866520 in words is "twenty-one million, eight hundred sixty-six thousand, five hundred twenty".