21578868 has 18 divisors (see below), whose sum is σ = 54546674. Its totient is φ = 7192944.

The previous prime is 21578863. The next prime is 21578903. The reversal of 21578868 is 86887512.

It can be written as a sum of positive squares in only one way, i.e., 20903184 + 675684 = 4572^2 + 822^2 .

It is a tau number, because it is divible by the number of its divisors (18).

It is a super-2 number, since 2×21578868² = 931295088322848, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21578861) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 299671 + ... + 299742.

Almost surely, 2^21578868 is an apocalyptic number.

It is an amenable number.

21578868 is an abundant number, since it is smaller than the sum of its proper divisors (32967806).

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

21578868 is a wasteful number, since it uses less digits than its factorization.

21578868 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 599423 (or 599418 counting only the distinct ones).

The product of its digits is 215040, while the sum is 45.

The square root of 21578868 is about 4645.3060179067. The cubic root of 21578868 is about 278.4044799616.

It can be divided in two parts, 2157 and 8868, that added together give a square (11025 = 105²).

The spelling of 21578868 in words is "twenty-one million, five hundred seventy-eight thousand, eight hundred sixty-eight".