641887999981 has 2 divisors, whose sum is σ = 641887999982. Its totient is φ = 641887999980.

The previous prime is 641887999979. The next prime is 641888000009. The reversal of 641887999981 is 189999788146.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 409684484356 + 232203515625 = 640066^2 + 481875^2 .

It is a cyclic number.

It is not a de Polignac number, because 641887999981 - 2¹ = 641887999979 is a prime.

It is a super-2 number, since 2×641887999981² (a number of 24 digits) contains 22 as substring.

Together with 641887999979, 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 (641887999901) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 320943999990 + 320943999991.

It is an arithmetic number, because the mean of its divisors is an integer number (320943999991).

Almost surely, 2^641887999981 is an apocalyptic number.

It is an amenable number.

641887999981 is a deficient number, since it is larger than the sum of its proper divisors (1).

641887999981 is an equidigital number, since it uses as much as digits as its factorization.

641887999981 is an evil number, because the sum of its binary digits is even.

The product of its digits is 564350976, while the sum is 79.

The spelling of 641887999981 in words is "six hundred forty-one billion, eight hundred eighty-seven million, nine hundred ninety-nine thousand, nine hundred eighty-one".