21015983 has 4 divisors (see below), whose sum is σ = 21026760. Its totient is φ = 21005208.

The previous prime is 21015971. The next prime is 21016007. The reversal of 21015983 is 38951012.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 21015983 - 2¹⁸ = 20753839 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21015913) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1553 + ... + 6666.

It is an arithmetic number, because the mean of its divisors is an integer number (5256690).

Almost surely, 2^21015983 is an apocalyptic number.

21015983 is a deficient number, since it is larger than the sum of its proper divisors (10777).

21015983 is an equidigital number, since it uses as much as digits as its factorization.

21015983 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10776.

The product of its (nonzero) digits is 2160, while the sum is 29.

The square root of 21015983 is about 4584.3192515356. The cubic root of 21015983 is about 275.9623933568.

Adding to 21015983 its reverse (38951012), we get a palindrome (59966995).

The spelling of 21015983 in words is "twenty-one million, fifteen thousand, nine hundred eighty-three".