646955821 has 2 divisors, whose sum is σ = 646955822. Its totient is φ = 646955820.

The previous prime is 646955807. The next prime is 646955831. The reversal of 646955821 is 128559646.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 636805225 + 10150596 = 25235^2 + 3186^2 .

It is a cyclic number.

It is not a de Polignac number, because 646955821 - 2¹³ = 646947629 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (646955831) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 323477910 + 323477911.

It is an arithmetic number, because the mean of its divisors is an integer number (323477911).

Almost surely, 2^646955821 is an apocalyptic number.

It is an amenable number.

646955821 is a deficient number, since it is larger than the sum of its proper divisors (1).

646955821 is an equidigital number, since it uses as much as digits as its factorization.

646955821 is an evil number, because the sum of its binary digits is even.

The product of its digits is 518400, while the sum is 46.

The square root of 646955821 is about 25435.3262412732. The cubic root of 646955821 is about 864.8846877593.

The spelling of 646955821 in words is "six hundred forty-six million, nine hundred fifty-five thousand, eight hundred twenty-one".