21207240 has 48 divisors (see below), whose sum is σ = 68924700. Its totient is φ = 5655168.

The previous prime is 21207239. The next prime is 21207259. The reversal of 21207240 is 4270212.

It can be written as a sum of positive squares in 2 ways, for example, as 17589636 + 3617604 = 4194^2 + 1902^2 .

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

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, 29095 + ... + 29814.

Almost surely, 2^21207240 is an apocalyptic number.

21207240 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21207240 is an abundant number, since it is smaller than the sum of its proper divisors (47717460).

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

21207240 is a wasteful number, since it uses less digits than its factorization.

21207240 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 58926 (or 58919 counting only the distinct ones).

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

The square root of 21207240 is about 4605.1319199345. The cubic root of 21207240 is about 276.7970031529.

Adding to 21207240 its reverse (4270212), we get a palindrome (25477452).

The spelling of 21207240 in words is "twenty-one million, two hundred seven thousand, two hundred forty".