21510864 has 30 divisors (see below), whose sum is σ = 60200946. Its totient is φ = 7170240.

The previous prime is 21510859. The next prime is 21510883. The reversal of 21510864 is 46801512.

It can be written as a sum of positive squares in only one way, i.e., 21344400 + 166464 = 4620^2 + 408^2 .

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 74547 + ... + 74834.

Almost surely, 2^21510864 is an apocalyptic number.

21510864 is a gapful number since it is divisible by the number (24) formed by its first and last digit.

It is an amenable number.

21510864 is an abundant number, since it is smaller than the sum of its proper divisors (38690082).

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

21510864 is a wasteful number, since it uses less digits than its factorization.

21510864 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 149395 (or 149386 counting only the distinct ones).

The product of its (nonzero) digits is 1920, while the sum is 27.

The square root of 21510864 is about 4637.9805950435. The cubic root of 21510864 is about 278.1117160511. Note that the first 3 decimals are identical.

The spelling of 21510864 in words is "twenty-one million, five hundred ten thousand, eight hundred sixty-four".