641661721 has 2 divisors, whose sum is σ = 641661722. Its totient is φ = 641661720.

The previous prime is 641661697. The next prime is 641661737. The reversal of 641661721 is 127166146.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 490002496 + 151659225 = 22136^2 + 12315^2 .

It is a cyclic number.

It is not a de Polignac number, because 641661721 - 2⁵ = 641661689 is a prime.

It is not a weakly prime, because it can be changed into another prime (641661791) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 320830860 + 320830861.

It is an arithmetic number, because the mean of its divisors is an integer number (320830861).

Almost surely, 2^641661721 is an apocalyptic number.

It is an amenable number.

641661721 is a deficient number, since it is larger than the sum of its proper divisors (1).

641661721 is an equidigital number, since it uses as much as digits as its factorization.

641661721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 12096, while the sum is 34.

The square root of 641661721 is about 25331.0426354700. The cubic root of 641661721 is about 862.5190792111.

The spelling of 641661721 in words is "six hundred forty-one million, six hundred sixty-one thousand, seven hundred twenty-one".