641681 has 2 divisors, whose sum is σ = 641682. Its totient is φ = 641680.

The previous prime is 641639. The next prime is 641701. The reversal of 641681 is 186146.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 640000 + 1681 = 800^2 + 41^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-641681 is a prime.

It is a super-2 number, since 2×641681² = 823509011522, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 641681.

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

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 320840 + 320841.

It is an arithmetic number, because the mean of its divisors is an integer number (320841).

2⁶⁴¹⁶⁸¹ is an apocalyptic number.

It is an amenable number.

641681 is a deficient number, since it is larger than the sum of its proper divisors (1).

641681 is an equidigital number, since it uses as much as digits as its factorization.

641681 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1152, while the sum is 26.

The square root of 641681 is about 801.0499360215. The cubic root of 641681 is about 86.2527717376.

Subtracting from 641681 its reverse (186146), we obtain a triangular number (455535 = T₉₅₄).

It can be divided in two parts, 64 and 1681, that multiplied together give a square (107584 = 328²).

The spelling of 641681 in words is "six hundred forty-one thousand, six hundred eighty-one".