21387240 has 320 divisors, whose sum is σ = 87816960. Its totient is φ = 4561920.

The previous prime is 21387227. The next prime is 21387251. The reversal of 21387240 is 4278312.

It is a hoax number, since the sum of its digits (27) coincides with the sum of the digits of its distinct prime factors.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 79 ways as a sum of consecutive naturals, for example, 521620 + ... + 521660.

It is an arithmetic number, because the mean of its divisors is an integer number (274428).

Almost surely, 2^21387240 is an apocalyptic number.

21387240 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21387240, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (43908480).

21387240 is an abundant number, since it is smaller than the sum of its proper divisors (66429720).

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

21387240 is a wasteful number, since it uses less digits than its factorization.

21387240 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 94 (or 81 counting only the distinct ones).

The product of its (nonzero) digits is 2688, while the sum is 27.

The square root of 21387240 is about 4624.6340395755. The cubic root of 21387240 is about 277.5779182218.

The spelling of 21387240 in words is "twenty-one million, three hundred eighty-seven thousand, two hundred forty".