641521661 has 4 divisors (see below), whose sum is σ = 699841824. Its totient is φ = 583201500.

The previous prime is 641521631. The next prime is 641521667. The reversal of 641521661 is 166125146.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 641521661 - 2⁶ = 641521597 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (641521667) 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, 29160065 + ... + 29160086.

It is an arithmetic number, because the mean of its divisors is an integer number (174960456).

Almost surely, 2^641521661 is an apocalyptic number.

It is an amenable number.

641521661 is a deficient number, since it is larger than the sum of its proper divisors (58320163).

641521661 is a wasteful number, since it uses less digits than its factorization.

641521661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 58320162.

The product of its digits is 8640, while the sum is 32.

The square root of 641521661 is about 25328.2778925058. The cubic root of 641521661 is about 862.4563186167.

The spelling of 641521661 in words is "six hundred forty-one million, five hundred twenty-one thousand, six hundred sixty-one".