21370721 has 2 divisors, whose sum is σ = 21370722. Its totient is φ = 21370720.

The previous prime is 21370693. The next prime is 21370729. The reversal of 21370721 is 12707312.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17106496 + 4264225 = 4136^2 + 2065^2 .

It is a cyclic number.

It is not a de Polignac number, because 21370721 - 2¹⁴ = 21354337 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (21370729) 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, 10685360 + 10685361.

It is an arithmetic number, because the mean of its divisors is an integer number (10685361).

Almost surely, 2^21370721 is an apocalyptic number.

It is an amenable number.

21370721 is a deficient number, since it is larger than the sum of its proper divisors (1).

21370721 is an equidigital number, since it uses as much as digits as its factorization.

21370721 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 588, while the sum is 23.

The square root of 21370721 is about 4622.8477154239. The cubic root of 21370721 is about 277.5064349345.

The spelling of 21370721 in words is "twenty-one million, three hundred seventy thousand, seven hundred twenty-one".