21615240 has 128 divisors (see below), whose sum is σ = 68428800. Its totient is φ = 5456640.

The previous prime is 21615233. The next prime is 21615247. The reversal of 21615240 is 4251612.

It is an interprime number because it is at equal distance from previous prime (21615233) and next prime (21615247).

It is not an unprimeable number, because it can be changed into a prime (21615247) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 304405 + ... + 304475.

It is an arithmetic number, because the mean of its divisors is an integer number (534600).

Almost surely, 2^21615240 is an apocalyptic number.

21615240 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 21615240, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (34214400).

21615240 is an abundant number, since it is smaller than the sum of its proper divisors (46813560).

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

21615240 is a wasteful number, since it uses less digits than its factorization.

21615240 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 187 (or 183 counting only the distinct ones).

The product of its (nonzero) digits is 480, while the sum is 21.

The square root of 21615240 is about 4649.2192893001. The cubic root of 21615240 is about 278.5608125944.

Adding to 21615240 its reverse (4251612), we get a palindrome (25866852).

The spelling of 21615240 in words is "twenty-one million, six hundred fifteen thousand, two hundred forty".