21540240 has 60 divisors (see below), whose sum is σ = 72341724. Its totient is φ = 5743872.

The previous prime is 21540229. The next prime is 21540247. The reversal of 21540240 is 4204512.

It can be written as a sum of positive squares in 2 ways, for example, as 14379264 + 7160976 = 3792^2 + 2676^2 .

It is a tau number, because it is divible by the number of its divisors (60).

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

It is not an unprimeable number, because it can be changed into a prime (21540247) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 14239 + ... + 15678.

Almost surely, 2^21540240 is an apocalyptic number.

21540240 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21540240 is an abundant number, since it is smaller than the sum of its proper divisors (50801484).

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

21540240 is a wasteful number, since it uses less digits than its factorization.

21540240 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 29936 (or 29927 counting only the distinct ones).

The product of its (nonzero) digits is 320, while the sum is 18.

The square root of 21540240 is about 4641.1464101017. The cubic root of 21540240 is about 278.2382582113.

Adding to 21540240 its reverse (4204512), we get a palindrome (25744752).

The spelling of 21540240 in words is "twenty-one million, five hundred forty thousand, two hundred forty".