21793721 has 2 divisors, whose sum is σ = 21793722. Its totient is φ = 21793720.

The previous prime is 21793699. The next prime is 21793747. The reversal of 21793721 is 12739712.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17106496 + 4687225 = 4136^2 + 2165^2 .

It is a cyclic number.

It is not a de Polignac number, because 21793721 - 2⁶ = 21793657 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21793781) 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 as a sum of consecutive naturals, namely, 10896860 + 10896861.

It is an arithmetic number, because the mean of its divisors is an integer number (10896861).

Almost surely, 2^21793721 is an apocalyptic number.

It is an amenable number.

21793721 is a deficient number, since it is larger than the sum of its proper divisors (1).

21793721 is an equidigital number, since it uses as much as digits as its factorization.

21793721 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 5292, while the sum is 32.

The square root of 21793721 is about 4668.3745565239. The cubic root of 21793721 is about 279.3254211710.

The spelling of 21793721 in words is "twenty-one million, seven hundred ninety-three thousand, seven hundred twenty-one".