21518240 has 24 divisors (see below), whose sum is σ = 50837220. Its totient is φ = 8607232.

The previous prime is 21518239. The next prime is 21518267. The reversal of 21518240 is 4281512.

It can be written as a sum of positive squares in 2 ways, for example, as 21418384 + 99856 = 4628^2 + 316^2 .

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, 67085 + ... + 67404.

Almost surely, 2^21518240 is an apocalyptic number.

21518240 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21518240 is an abundant number, since it is smaller than the sum of its proper divisors (29318980).

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

21518240 is a wasteful number, since it uses less digits than its factorization.

21518240 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 134504 (or 134496 counting only the distinct ones).

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

The square root of 21518240 is about 4638.7757005486. The cubic root of 21518240 is about 278.1435002633.

Adding to 21518240 its reverse (4281512), we get a palindrome (25799752).

The spelling of 21518240 in words is "twenty-one million, five hundred eighteen thousand, two hundred forty".