21517240 has 32 divisors (see below), whose sum is σ = 51263280. Its totient is φ = 8100352.

The previous prime is 21517231. The next prime is 21517247. The reversal of 21517240 is 4271512.

It is a happy number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21517247) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 15142 + ... + 16501.

Almost surely, 2^21517240 is an apocalyptic number.

21517240 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21517240 is an abundant number, since it is smaller than the sum of its proper divisors (29746040).

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

21517240 is a wasteful number, since it uses less digits than its factorization.

21517240 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 31671 (or 31667 counting only the distinct ones).

The product of its (nonzero) digits is 560, while the sum is 22.

The square root of 21517240 is about 4638.6679122351. The cubic root of 21517240 is about 278.1391915496.

Adding to 21517240 its reverse (4271512), we get a palindrome (25788752).

The spelling of 21517240 in words is "twenty-one million, five hundred seventeen thousand, two hundred forty".