820555721 has 2 divisors, whose sum is σ = 820555722. Its totient is φ = 820555720.

The previous prime is 820555693. The next prime is 820555753. The reversal of 820555721 is 127555028.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 661518400 + 159037321 = 25720^2 + 12611^2 .

It is a cyclic number.

It is not a de Polignac number, because 820555721 - 2¹⁰ = 820554697 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (820555121) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 410277860 + 410277861.

It is an arithmetic number, because the mean of its divisors is an integer number (410277861).

Almost surely, 2^820555721 is an apocalyptic number.

It is an amenable number.

820555721 is a deficient number, since it is larger than the sum of its proper divisors (1).

820555721 is an equidigital number, since it uses as much as digits as its factorization.

820555721 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 28000, while the sum is 35.

The square root of 820555721 is about 28645.3437926655. The cubic root of 820555721 is about 936.2015574076.

The spelling of 820555721 in words is "eight hundred twenty million, five hundred fifty-five thousand, seven hundred twenty-one".