21040240 has 40 divisors (see below), whose sum is σ = 52684128. Its totient is φ = 7768320.

The previous prime is 21040231. The next prime is 21040247. The reversal of 21040240 is 4204012.

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

It is a Harshad number since it is a multiple of its sum of digits (13).

It is a self number, because there is not a number n which added to its sum of digits gives 21040240.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21040247) 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, 9076 + ... + 11155.

Almost surely, 2^21040240 is an apocalyptic number.

21040240 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21040240 is an abundant number, since it is smaller than the sum of its proper divisors (31643888).

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

21040240 is a wasteful number, since it uses less digits than its factorization.

21040240 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 20257 (or 20251 counting only the distinct ones).

The product of its (nonzero) digits is 64, while the sum is 13.

The square root of 21040240 is about 4586.9641376405. The cubic root of 21040240 is about 276.0685260079.

Adding to 21040240 its reverse (4204012), we get a palindrome (25244252).

The spelling of 21040240 in words is "twenty-one million, forty thousand, two hundred forty".