21083721 has 4 divisors (see below), whose sum is σ = 28111632. Its totient is φ = 14055812.

The previous prime is 21083719. The next prime is 21083773. The reversal of 21083721 is 12738012.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21083721 - 2¹ = 21083719 is a prime.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 21083691 and 21083700.

It is not an unprimeable number, because it can be changed into a prime (21085721) 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 in 3 ways as a sum of consecutive naturals, for example, 3513951 + ... + 3513956.

It is an arithmetic number, because the mean of its divisors is an integer number (7027908).

Almost surely, 2^21083721 is an apocalyptic number.

It is an amenable number.

21083721 is a deficient number, since it is larger than the sum of its proper divisors (7027911).

21083721 is an equidigital number, since it uses as much as digits as its factorization.

21083721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7027910.

The product of its (nonzero) digits is 672, while the sum is 24.

The square root of 21083721 is about 4591.7013186835. The cubic root of 21083721 is about 276.2585662393.

The spelling of 21083721 in words is "twenty-one million, eighty-three thousand, seven hundred twenty-one".