21895566 has 64 divisors (see below), whose sum is σ = 55351296. Its totient is φ = 5608800.

The previous prime is 21895553. The next prime is 21895567. The reversal of 21895566 is 66559812.

It is a Harshad number since it is a multiple of its sum of digits (42).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21895567) 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, 38061 + ... + 38631.

It is an arithmetic number, because the mean of its divisors is an integer number (864864).

Almost surely, 2^21895566 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21895566, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27675648).

21895566 is an abundant number, since it is smaller than the sum of its proper divisors (33455730).

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

21895566 is a wasteful number, since it uses less digits than its factorization.

21895566 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 677.

The product of its digits is 129600, while the sum is 42.

The square root of 21895566 is about 4679.2698148322. The cubic root of 21895566 is about 279.7598536174.

The spelling of 21895566 in words is "twenty-one million, eight hundred ninety-five thousand, five hundred sixty-six".