21315840 has 288 divisors, whose sum is σ = 85161216. Its totient is φ = 4423680.

The previous prime is 21315823. The next prime is 21315883. The reversal of 21315840 is 4851312.

It is a Harshad number since it is a multiple of its sum of digits (24).

It is a self number, because there is not a number n which added to its sum of digits gives 21315840.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 349410 + ... + 349470.

Almost surely, 2^21315840 is an apocalyptic number.

21315840 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 21315840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (42580608).

21315840 is an abundant number, since it is smaller than the sum of its proper divisors (63845376).

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

21315840 is a wasteful number, since it uses less digits than its factorization.

21315840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 105 (or 91 counting only the distinct ones).

The product of its (nonzero) digits is 960, while the sum is 24.

The square root of 21315840 is about 4616.9080562645. The cubic root of 21315840 is about 277.2686815108.

It can be divided in two parts, 21315 and 840, that added together give a triangular number (22155 = T₂₁₀).

The spelling of 21315840 in words is "twenty-one million, three hundred fifteen thousand, eight hundred forty".