21245640 has 64 divisors (see below), whose sum is σ = 68644800. Its totient is φ = 5229312.

The previous prime is 21245617. The next prime is 21245669. The reversal of 21245640 is 4654212.

It is a Harshad number since it is a multiple of its sum of digits (24).

It is a self number, because there is not a number n which added to its sum of digits gives 21245640.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 5250 + ... + 8369.

It is an arithmetic number, because the mean of its divisors is an integer number (1072575).

Almost surely, 2^21245640 is an apocalyptic number.

21245640 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21245640 is an abundant number, since it is smaller than the sum of its proper divisors (47399160).

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

21245640 is a wasteful number, since it uses less digits than its factorization.

21245640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 13646 (or 13642 counting only the distinct ones).

The product of its (nonzero) digits is 1920, while the sum is 24.

The square root of 21245640 is about 4609.2992959885. The cubic root of 21245640 is about 276.9639680832.

Adding to 21245640 its reverse (4654212), we get a palindrome (25899852).

The spelling of 21245640 in words is "twenty-one million, two hundred forty-five thousand, six hundred forty".