21504040 has 32 divisors (see below), whose sum is σ = 48518280. Its totient is φ = 8577792.

The previous prime is 21504023. The next prime is 21504047. The reversal of 21504040 is 4040512.

It can be written as a sum of positive squares in 4 ways, for example, as 13853284 + 7650756 = 3722^2 + 2766^2 .

It is not an unprimeable number, because it can be changed into a prime (21504047) 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, 24082 + ... + 24958.

Almost surely, 2^21504040 is an apocalyptic number.

21504040 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21504040 is an abundant number, since it is smaller than the sum of its proper divisors (27014240).

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

21504040 is a wasteful number, since it uses less digits than its factorization.

21504040 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1501 (or 1497 counting only the distinct ones).

The product of its (nonzero) digits is 160, while the sum is 16.

The square root of 21504040 is about 4637.2448716884. The cubic root of 21504040 is about 278.0823040128.

Adding to 21504040 its reverse (4040512), we get a palindrome (25544552).

The spelling of 21504040 in words is "twenty-one million, five hundred four thousand, forty".