21251840 has 36 divisors (see below), whose sum is σ = 50907864. Its totient is φ = 8500224.

The previous prime is 21251837. The next prime is 21251843. The reversal of 21251840 is 4815212.

It is an interprime number because it is at equal distance from previous prime (21251837) and next prime (21251843).

It is a hoax number, since the sum of its digits (23) coincides with the sum of the digits of its distinct prime factors.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21251843) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 7022 + ... + 9581.

Almost surely, 2^21251840 is an apocalyptic number.

21251840 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21251840 is an abundant number, since it is smaller than the sum of its proper divisors (29656024).

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

21251840 is an equidigital number, since it uses as much as digits as its factorization.

21251840 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 16624 (or 16610 counting only the distinct ones).

The product of its (nonzero) digits is 640, while the sum is 23.

The square root of 21251840 is about 4609.9718003476. The cubic root of 21251840 is about 276.9909070942.

The spelling of 21251840 in words is "twenty-one million, two hundred fifty-one thousand, eight hundred forty".