643781 has 2 divisors, whose sum is σ = 643782. Its totient is φ = 643780.

The previous prime is 643751. The next prime is 643847. The reversal of 643781 is 187346.

643781 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 616225 + 27556 = 785^2 + 166^2 .

It is a cyclic number.

It is not a de Polignac number, because 643781 - 2¹⁸ = 381637 is a prime.

It is a super-2 number, since 2×643781² = 828907951922, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 643781.

It is not a weakly prime, because it can be changed into another prime (643751) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 321890 + 321891.

It is an arithmetic number, because the mean of its divisors is an integer number (321891).

2⁶⁴³⁷⁸¹ is an apocalyptic number.

It is an amenable number.

643781 is a deficient number, since it is larger than the sum of its proper divisors (1).

643781 is an equidigital number, since it uses as much as digits as its factorization.

643781 is an evil number, because the sum of its binary digits is even.

The product of its digits is 4032, while the sum is 29.

The square root of 643781 is about 802.3596450470. The cubic root of 643781 is about 86.3467611115.

The spelling of 643781 in words is "six hundred forty-three thousand, seven hundred eighty-one".