641565781 has 2 divisors, whose sum is σ = 641565782. Its totient is φ = 641565780.

The previous prime is 641565779. The next prime is 641565791. The reversal of 641565781 is 187565146.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 368985681 + 272580100 = 19209^2 + 16510^2 .

It is a cyclic number.

It is not a de Polignac number, because 641565781 - 2¹ = 641565779 is a prime.

It is a super-2 number, since 2×641565781² = 823213302700279922, which contains 22 as substring.

Together with 641565779, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (641565721) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 320782890 + 320782891.

It is an arithmetic number, because the mean of its divisors is an integer number (320782891).

Almost surely, 2^641565781 is an apocalyptic number.

It is an amenable number.

641565781 is a deficient number, since it is larger than the sum of its proper divisors (1).

641565781 is an equidigital number, since it uses as much as digits as its factorization.

641565781 is an evil number, because the sum of its binary digits is even.

The product of its digits is 201600, while the sum is 43.

The square root of 641565781 is about 25329.1488408118. The cubic root of 641565781 is about 862.4760896823.

The spelling of 641565781 in words is "six hundred forty-one million, five hundred sixty-five thousand, seven hundred eighty-one".