21270240 has 72 divisors (see below), whose sum is σ = 72589608. Its totient is φ = 5671680.

The previous prime is 21270233. The next prime is 21270269. The reversal of 21270240 is 4207212.

It is a tau number, because it is divible by the number of its divisors (72).

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 5946 + ... + 8825.

It is an arithmetic number, because the mean of its divisors is an integer number (1008189).

Almost surely, 2^21270240 is an apocalyptic number.

21270240 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21270240 is an abundant number, since it is smaller than the sum of its proper divisors (51319368).

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

21270240 is a wasteful number, since it uses less digits than its factorization.

21270240 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 14792 (or 14781 counting only the distinct ones).

The product of its (nonzero) digits is 224, while the sum is 18.

The square root of 21270240 is about 4611.9670423801. The cubic root of 21270240 is about 277.0708242919.

Adding to 21270240 its reverse (4207212), we get a palindrome (25477452).

The spelling of 21270240 in words is "twenty-one million, two hundred seventy thousand, two hundred forty".