21003640 has 32 divisors (see below), whose sum is σ = 54010080. Its totient is φ = 7201152.

The previous prime is 21003637. The next prime is 21003659. The reversal of 21003640 is 4630012.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 37227 + ... + 37786.

It is an arithmetic number, because the mean of its divisors is an integer number (1687815).

Almost surely, 2^21003640 is an apocalyptic number.

21003640 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21003640 is an abundant number, since it is smaller than the sum of its proper divisors (33006440).

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

21003640 is a wasteful number, since it uses less digits than its factorization.

21003640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 75031 (or 75027 counting only the distinct ones).

The product of its (nonzero) digits is 144, while the sum is 16.

The square root of 21003640 is about 4582.9728343074. The cubic root of 21003640 is about 275.9083571680.

Adding to 21003640 its reverse (4630012), we get a palindrome (25633652).

The spelling of 21003640 in words is "twenty-one million, three thousand, six hundred forty".