21040640 has 40 divisors (see below), whose sum is σ = 50454360. Its totient is φ = 8415232.

The previous prime is 21040633. The next prime is 21040651. The reversal of 21040640 is 4604012.

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

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, 1550 + ... + 6669.

It is an arithmetic number, because the mean of its divisors is an integer number (1261359).

Almost surely, 2^21040640 is an apocalyptic number.

21040640 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21040640 is an abundant number, since it is smaller than the sum of its proper divisors (29413720).

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

21040640 is an frugal number, since it uses more digits than its factorization.

21040640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8242 (or 8226 counting only the distinct ones).

The product of its (nonzero) digits is 192, while the sum is 17.

The square root of 21040640 is about 4587.0077392566. The cubic root of 21040640 is about 276.0702754606.

Adding to 21040640 its reverse (4604012), we get a palindrome (25644652).

The spelling of 21040640 in words is "twenty-one million, forty thousand, six hundred forty".