21440240 has 20 divisors (see below), whose sum is σ = 49848744. Its totient is φ = 8576064.

The previous prime is 21440239. The next prime is 21440257. The reversal of 21440240 is 4204412.

It is a tau number, because it is divible by the number of its divisors (20).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 133922 + ... + 134081.

Almost surely, 2^21440240 is an apocalyptic number.

21440240 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21440240 is an abundant number, since it is smaller than the sum of its proper divisors (28408504).

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

21440240 is a wasteful number, since it uses less digits than its factorization.

21440240 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 268016 (or 268010 counting only the distinct ones).

The product of its (nonzero) digits is 256, while the sum is 17.

The square root of 21440240 is about 4630.3606770963. The cubic root of 21440240 is about 277.8070189069.

Adding to 21440240 its reverse (4204412), we get a palindrome (25644652).

The spelling of 21440240 in words is "twenty-one million, four hundred forty thousand, two hundred forty".