641981 has 2 divisors, whose sum is σ = 641982. Its totient is φ = 641980.

The previous prime is 641969. The next prime is 642011. The reversal of 641981 is 189146.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 586756 + 55225 = 766^2 + 235^2 .

It is a cyclic number.

It is not a de Polignac number, because 641981 - 2¹⁰ = 640957 is a prime.

It is a super-2 number, since 2×641981² = 824279208722, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (641581) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 320990 + 320991.

It is an arithmetic number, because the mean of its divisors is an integer number (320991).

2⁶⁴¹⁹⁸¹ is an apocalyptic number.

It is an amenable number.

641981 is a deficient number, since it is larger than the sum of its proper divisors (1).

641981 is an equidigital number, since it uses as much as digits as its factorization.

641981 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1728, while the sum is 29.

The square root of 641981 is about 801.2371683840. The cubic root of 641981 is about 86.2662113335.

The spelling of 641981 in words is "six hundred forty-one thousand, nine hundred eighty-one".