21718564 has 36 divisors (see below), whose sum is σ = 45749340. Its totient is φ = 8984640.

The previous prime is 21718553. The next prime is 21718583. The reversal of 21718564 is 46581712.

It can be written as a sum of positive squares in 2 ways, for example, as 15920100 + 5798464 = 3990^2 + 2408^2 .

It is a hoax number, since the sum of its digits (34) coincides with the sum of the digits of its distinct prime factors.

It is an unprimeable number.

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 11 ways as a sum of consecutive naturals, for example, 3774 + ... + 7594.

It is an arithmetic number, because the mean of its divisors is an integer number (1270815).

Almost surely, 2^21718564 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 21718564, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (22874670).

21718564 is an abundant number, since it is smaller than the sum of its proper divisors (24030776).

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

21718564 is a wasteful number, since it uses less digits than its factorization.

21718564 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3868 (or 3859 counting only the distinct ones).

The product of its digits is 13440, while the sum is 34.

The square root of 21718564 is about 4660.3180148998. The cubic root of 21718564 is about 279.0039610097.

It can be divided in two parts, 217 and 18564, that added together give a palindrome (18781).

The spelling of 21718564 in words is "twenty-one million, seven hundred eighteen thousand, five hundred sixty-four".