21243730 has 16 divisors (see below), whose sum is σ = 38763864. Its totient is φ = 8380800.

The previous prime is 21243721. The next prime is 21243731. The reversal of 21243730 is 3734212.

It can be written as a sum of positive squares in 4 ways, for example, as 10804369 + 10439361 = 3287^2 + 3231^2 .

It is not an unprimeable number, because it can be changed into a prime (21243731) 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, 13821 + ... + 15280.

Almost surely, 2^21243730 is an apocalyptic number.

21243730 is a deficient number, since it is larger than the sum of its proper divisors (17520134).

21243730 is a wasteful number, since it uses less digits than its factorization.

21243730 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 29181.

The product of its (nonzero) digits is 1008, while the sum is 22.

The square root of 21243730 is about 4609.0921014881. The cubic root of 21243730 is about 276.9556680738.

Adding to 21243730 its reverse (3734212), we get a palindrome (24977942).

The spelling of 21243730 in words is "twenty-one million, two hundred forty-three thousand, seven hundred thirty".