21255418 has 4 divisors (see below), whose sum is σ = 31883130. Its totient is φ = 10627708.

The previous prime is 21255407. The next prime is 21255419. The reversal of 21255418 is 81455212.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in only one way, i.e., 20007729 + 1247689 = 4473^2 + 1117^2 .

It is not an unprimeable number, because it can be changed into a prime (21255419) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5313853 + ... + 5313856.

Almost surely, 2^21255418 is an apocalyptic number.

21255418 is a deficient number, since it is larger than the sum of its proper divisors (10627712).

21255418 is a wasteful number, since it uses less digits than its factorization.

21255418 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10627711.

The product of its digits is 3200, while the sum is 28.

The square root of 21255418 is about 4610.3598558030. The cubic root of 21255418 is about 277.0064511263.

The spelling of 21255418 in words is "twenty-one million, two hundred fifty-five thousand, four hundred eighteen".