21018938 has 4 divisors (see below), whose sum is σ = 31528410. Its totient is φ = 10509468.

The previous prime is 21018931. The next prime is 21018947. The reversal of 21018938 is 83981012.

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., 15031129 + 5987809 = 3877^2 + 2447^2 .

It is not an unprimeable number, because it can be changed into a prime (21018931) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5254733 + ... + 5254736.

Almost surely, 2^21018938 is an apocalyptic number.

21018938 is a deficient number, since it is larger than the sum of its proper divisors (10509472).

21018938 is a wasteful number, since it uses less digits than its factorization.

21018938 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10509471.

The product of its (nonzero) digits is 3456, while the sum is 32.

The square root of 21018938 is about 4584.6415345150. The cubic root of 21018938 is about 275.9753268569.

The spelling of 21018938 in words is "twenty-one million, eighteen thousand, nine hundred thirty-eight".