646105721 has 2 divisors, whose sum is σ = 646105722. Its totient is φ = 646105720.

The previous prime is 646105709. The next prime is 646105841. The reversal of 646105721 is 127501646.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 390457600 + 255648121 = 19760^2 + 15989^2 .

It is a cyclic number.

It is not a de Polignac number, because 646105721 - 2⁶ = 646105657 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 (646108721) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 323052860 + 323052861.

It is an arithmetic number, because the mean of its divisors is an integer number (323052861).

Almost surely, 2^646105721 is an apocalyptic number.

It is an amenable number.

646105721 is a deficient number, since it is larger than the sum of its proper divisors (1).

646105721 is an equidigital number, since it uses as much as digits as its factorization.

646105721 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 10080, while the sum is 32.

The square root of 646105721 is about 25418.6097377492. The cubic root of 646105721 is about 864.5057021990.

The spelling of 646105721 in words is "six hundred forty-six million, one hundred five thousand, seven hundred twenty-one".