21208740 has 48 divisors (see below), whose sum is σ = 67869312. Its totient is φ = 4847616.

The previous prime is 21208739. The next prime is 21208751. The reversal of 21208740 is 4780212.

It is a self number, because there is not a number n which added to its sum of digits gives 21208740.

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, 24829 + ... + 25668.

It is an arithmetic number, because the mean of its divisors is an integer number (1413944).

Almost surely, 2^21208740 is an apocalyptic number.

21208740 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21208740 is an abundant number, since it is smaller than the sum of its proper divisors (46660572).

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

21208740 is a wasteful number, since it uses less digits than its factorization.

21208740 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 50516 (or 50514 counting only the distinct ones).

The product of its (nonzero) digits is 896, while the sum is 24.

The square root of 21208740 is about 4605.2947788388. The cubic root of 21208740 is about 276.8035290015.

Adding to 21208740 its reverse (4780212), we get a palindrome (25988952).

The spelling of 21208740 in words is "twenty-one million, two hundred eight thousand, seven hundred forty".