21220864 has 80 divisors (see below), whose sum is σ = 50282496. Its totient is φ = 8755200.

The previous prime is 21220861. The next prime is 21220867. The reversal of 21220864 is 46802212.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (21220861) and next prime (21220867).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21220861) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 111009 + ... + 111199.

Almost surely, 2^21220864 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 21220864, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25141248).

21220864 is an abundant number, since it is smaller than the sum of its proper divisors (29061632).

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

21220864 is an equidigital number, since it uses as much as digits as its factorization.

21220864 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 247 (or 231 counting only the distinct ones).

The product of its (nonzero) digits is 1536, while the sum is 25.

The square root of 21220864 is about 4606.6109017368. The cubic root of 21220864 is about 276.8562639700.

The spelling of 21220864 in words is "twenty-one million, two hundred twenty thousand, eight hundred sixty-four".