21895721 has 2 divisors, whose sum is σ = 21895722. Its totient is φ = 21895720.

The previous prime is 21895669. The next prime is 21895723. The reversal of 21895721 is 12759812.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21492496 + 403225 = 4636^2 + 635^2 .

It is a cyclic number.

It is not a de Polignac number, because 21895721 - 2¹⁴ = 21879337 is a prime.

Together with 21895723, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21895723) 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, 10947860 + 10947861.

It is an arithmetic number, because the mean of its divisors is an integer number (10947861).

Almost surely, 2^21895721 is an apocalyptic number.

It is an amenable number.

21895721 is a deficient number, since it is larger than the sum of its proper divisors (1).

21895721 is an equidigital number, since it uses as much as digits as its factorization.

21895721 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 10080, while the sum is 35.

The square root of 21895721 is about 4679.2863772161. The cubic root of 21895721 is about 279.7605137613.

The spelling of 21895721 in words is "twenty-one million, eight hundred ninety-five thousand, seven hundred twenty-one".