21253840 has 40 divisors (see below), whose sum is σ = 51568128. Its totient is φ = 8131200.

The previous prime is 21253763. The next prime is 21253849. The reversal of 21253840 is 4835212.

It is a tau number, because it is divible by the number of its divisors (40).

It is a hoax number, since the sum of its digits (25) 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 (21253849) 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, 3936 + ... + 7615.

Almost surely, 2^21253840 is an apocalyptic number.

21253840 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21253840 is an abundant number, since it is smaller than the sum of its proper divisors (30314288).

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

21253840 is a wasteful number, since it uses less digits than its factorization.

21253840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11587 (or 11581 counting only the distinct ones).

The product of its (nonzero) digits is 1920, while the sum is 25.

The square root of 21253840 is about 4610.1887163109. The cubic root of 21253840 is about 276.9995959801. Note that the first 3 decimals are identical.

It can be divided in two parts, 2 and 1253840, that multiplied together give a triangular number (2507680 = T₂₂₃₉).

The spelling of 21253840 in words is "twenty-one million, two hundred fifty-three thousand, eight hundred forty".