21318728 has 16 divisors (see below), whose sum is σ = 40289280. Its totient is φ = 10574928.

The previous prime is 21318727. The next prime is 21318733. The reversal of 21318728 is 82781312.

It is a junction number, because it is equal to n+sod(n) for n = 21318694 and 21318703.

It is not an unprimeable number, because it can be changed into a prime (21318727) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 9476 + ... + 11507.

It is an arithmetic number, because the mean of its divisors is an integer number (2518080).

Almost surely, 2^21318728 is an apocalyptic number.

It is an amenable number.

21318728 is a deficient number, since it is larger than the sum of its proper divisors (18970552).

21318728 is a wasteful number, since it uses less digits than its factorization.

21318728 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 21116 (or 21112 counting only the distinct ones).

The product of its digits is 5376, while the sum is 32.

The square root of 21318728 is about 4617.2208091015. The cubic root of 21318728 is about 277.2812029626.

The spelling of 21318728 in words is "twenty-one million, three hundred eighteen thousand, seven hundred twenty-eight".