21315240 has 48 divisors (see below), whose sum is σ = 69275700. Its totient is φ = 5683968.

The previous prime is 21315223. The next prime is 21315241. The reversal of 21315240 is 4251312.

It can be written as a sum of positive squares in 2 ways, for example, as 21288996 + 26244 = 4614^2 + 162^2 .

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

It is not an unprimeable number, because it can be changed into a prime (21315241) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 29245 + ... + 29964.

Almost surely, 2^21315240 is an apocalyptic number.

21315240 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21315240 is an abundant number, since it is smaller than the sum of its proper divisors (47960460).

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

21315240 is a wasteful number, since it uses less digits than its factorization.

21315240 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 59226 (or 59219 counting only the distinct ones).

The product of its (nonzero) digits is 240, while the sum is 18.

The square root of 21315240 is about 4616.8430772553. The cubic root of 21315240 is about 277.2660799592.

Adding to 21315240 its reverse (4251312), we get a palindrome (25566552).

The spelling of 21315240 in words is "twenty-one million, three hundred fifteen thousand, two hundred forty".