21218540 has 24 divisors (see below), whose sum is σ = 50924832. Its totient is φ = 7274880.

The previous prime is 21218521. The next prime is 21218551. The reversal of 21218540 is 4581212.

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, 75641 + ... + 75920.

It is an arithmetic number, because the mean of its divisors is an integer number (2121868).

Almost surely, 2^21218540 is an apocalyptic number.

21218540 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21218540 is an abundant number, since it is smaller than the sum of its proper divisors (29706292).

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

21218540 is a wasteful number, since it uses less digits than its factorization.

21218540 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 151577 (or 151575 counting only the distinct ones).

The product of its (nonzero) digits is 640, while the sum is 23.

The square root of 21218540 is about 4606.3586486508. The cubic root of 21218540 is about 276.8461569759.

Adding to 21218540 its reverse (4581212), we get a palindrome (25799752).

The spelling of 21218540 in words is "twenty-one million, two hundred eighteen thousand, five hundred forty".