21025664 has 64 divisors (see below), whose sum is σ = 46450800. Its totient is φ = 9400320.

The previous prime is 21025639. The next prime is 21025681. The reversal of 21025664 is 46652012.

It is a tau number, because it is divible by the number of its divisors (64).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 153404 + ... + 153540.

Almost surely, 2^21025664 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 21025664, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (23225400).

21025664 is an abundant number, since it is smaller than the sum of its proper divisors (25425136).

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

21025664 is a wasteful number, since it uses less digits than its factorization.

21025664 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 271 (or 259 counting only the distinct ones).

The product of its (nonzero) digits is 2880, while the sum is 26.

The square root of 21025664 is about 4585.3750119265. The cubic root of 21025664 is about 276.0047608225.

Adding to 21025664 its reverse (46652012), we get a palindrome (67677676).

The spelling of 21025664 in words is "twenty-one million, twenty-five thousand, six hundred sixty-four".