21715240 has 32 divisors (see below), whose sum is σ = 50054760. Its totient is φ = 8473600.

The previous prime is 21715231. The next prime is 21715247. The reversal of 21715240 is 4251712.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 18610596 + 3104644 = 4314^2 + 1762^2 .

It is not an unprimeable number, because it can be changed into a prime (21715247) 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, 4981 + ... + 8260.

Almost surely, 2^21715240 is an apocalyptic number.

21715240 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21715240 is an abundant number, since it is smaller than the sum of its proper divisors (28339520).

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

21715240 is a wasteful number, since it uses less digits than its factorization.

21715240 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 13293 (or 13289 counting only the distinct ones).

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

The square root of 21715240 is about 4659.9613732305. The cubic root of 21715240 is about 278.9897265437.

Adding to 21715240 its reverse (4251712), we get a palindrome (25966952).

The spelling of 21715240 in words is "twenty-one million, seven hundred fifteen thousand, two hundred forty".