21515040 has 144 divisors (see below), whose sum is σ = 74850048. Its totient is φ = 5626368.

The previous prime is 21515017. The next prime is 21515057. The reversal of 21515040 is 4051512.

It is a tau number, because it is divible by the number of its divisors (144).

It is a Harshad number since it is a multiple of its sum of digits (18).

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 96369 + ... + 96591.

It is an arithmetic number, because the mean of its divisors is an integer number (519792).

Almost surely, 2^21515040 is an apocalyptic number.

21515040 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 21515040, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (37425024).

21515040 is an abundant number, since it is smaller than the sum of its proper divisors (53335008).

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

21515040 is a wasteful number, since it uses less digits than its factorization.

21515040 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 311 (or 300 counting only the distinct ones).

The product of its (nonzero) digits is 200, while the sum is 18.

The square root of 21515040 is about 4638.4307691287. The cubic root of 21515040 is about 278.1297119094.

Adding to 21515040 its reverse (4051512), we get a palindrome (25566552).

The spelling of 21515040 in words is "twenty-one million, five hundred fifteen thousand, forty".