21215240 has 32 divisors (see below), whose sum is σ = 49383000. Its totient is φ = 8193024.

The previous prime is 21215237. The next prime is 21215261. The reversal of 21215240 is 4251212.

It can be written as a sum of positive squares in 4 ways, for example, as 20921476 + 293764 = 4574^2 + 542^2 .

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, 7985 + ... + 10304.

Almost surely, 2^21215240 is an apocalyptic number.

21215240 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21215240 is an abundant number, since it is smaller than the sum of its proper divisors (28167760).

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

21215240 is a wasteful number, since it uses less digits than its factorization.

21215240 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 18329 (or 18325 counting only the distinct ones).

The product of its (nonzero) digits is 160, while the sum is 17.

The square root of 21215240 is about 4606.0004342162. Note that the first 3 decimals coincide. The cubic root of 21215240 is about 276.8318041240.

Adding to 21215240 its reverse (4251212), we get a palindrome (25466452).

The spelling of 21215240 in words is "twenty-one million, two hundred fifteen thousand, two hundred forty".