641577721 has 4 divisors (see below), whose sum is σ = 641678500. Its totient is φ = 641476944.

The previous prime is 641577679. The next prime is 641577733. The reversal of 641577721 is 127775146.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 127775146 = 2 ⋅63887573.

It can be written as a sum of positive squares in 2 ways, for example, as 394459321 + 247118400 = 19861^2 + 15720^2 .

It is a cyclic number.

It is not a de Polignac number, because 641577721 - 2¹⁷ = 641446649 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (641577751) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 40146 + ... + 53803.

It is an arithmetic number, because the mean of its divisors is an integer number (160419625).

Almost surely, 2^641577721 is an apocalyptic number.

It is an amenable number.

641577721 is a deficient number, since it is larger than the sum of its proper divisors (100779).

641577721 is an equidigital number, since it uses as much as digits as its factorization.

641577721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 100778.

The product of its digits is 82320, while the sum is 40.

The square root of 641577721 is about 25329.3845365417. The cubic root of 641577721 is about 862.4814400823.

The spelling of 641577721 in words is "six hundred forty-one million, five hundred seventy-seven thousand, seven hundred twenty-one".