21515840 has 56 divisors (see below), whose sum is σ = 52011072. Its totient is φ = 8476160.

The previous prime is 21515831. The next prime is 21515843. The reversal of 21515840 is 4851512.

It is not an unprimeable number, because it can be changed into a prime (21515843) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 22247 + ... + 23193.

Almost surely, 2^21515840 is an apocalyptic number.

21515840 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 21515840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26005536).

21515840 is an abundant number, since it is smaller than the sum of its proper divisors (30495232).

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

21515840 is an equidigital number, since it uses as much as digits as its factorization.

21515840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1035 (or 1025 counting only the distinct ones).

The product of its (nonzero) digits is 1600, while the sum is 26.

The square root of 21515840 is about 4638.5170043884. The cubic root of 21515840 is about 278.1331591260.

The spelling of 21515840 in words is "twenty-one million, five hundred fifteen thousand, eight hundred forty".