641561 has 4 divisors (see below), whose sum is σ = 644112. Its totient is φ = 639012.

The previous prime is 641551. The next prime is 641579. The reversal of 641561 is 165146.

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 641561 - 2¹⁸ = 379417 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (641521) 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, 851 + ... + 1416.

It is an arithmetic number, because the mean of its divisors is an integer number (161028).

2⁶⁴¹⁵⁶¹ is an apocalyptic number.

It is an amenable number.

641561 is a deficient number, since it is larger than the sum of its proper divisors (2551).

641561 is a wasteful number, since it uses less digits than its factorization.

641561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2550.

The product of its digits is 720, while the sum is 23.

The square root of 641561 is about 800.9750308218. The cubic root of 641561 is about 86.2473947263.

The spelling of 641561 in words is "six hundred forty-one thousand, five hundred sixty-one".