21307240 has 32 divisors (see below), whose sum is σ = 48604680. Its totient is φ = 8404992.

The previous prime is 21307229. The next prime is 21307243. The reversal of 21307240 is 4270312.

It can be written as a sum of positive squares in 4 ways, for example, as 16208676 + 5098564 = 4026^2 + 2258^2 .

It is not an unprimeable number, because it can be changed into a prime (21307243) 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, 729 + ... + 6568.

Almost surely, 2^21307240 is an apocalyptic number.

21307240 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21307240 is an abundant number, since it is smaller than the sum of its proper divisors (27297440).

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

21307240 is a wasteful number, since it uses less digits than its factorization.

21307240 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7381 (or 7377 counting only the distinct ones).

The product of its (nonzero) digits is 336, while the sum is 19.

The square root of 21307240 is about 4615.9766030603. The cubic root of 21307240 is about 277.2313879392.

Adding to 21307240 its reverse (4270312), we get a palindrome (25577552).

The spelling of 21307240 in words is "twenty-one million, three hundred seven thousand, two hundred forty".