643778 has 4 divisors (see below), whose sum is σ = 965670. Its totient is φ = 321888.

The previous prime is 643751. The next prime is 643781. The reversal of 643778 is 877346.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in only one way, i.e., 344569 + 299209 = 587^2 + 547^2 .

It is a super-2 number, since 2×643778² = 828900226568, which contains 22 as substring.

It is a congruent number.

It is an unprimeable number.

643778 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 160943 + ... + 160946.

2⁶⁴³⁷⁷⁸ is an apocalyptic number.

643778 is a deficient number, since it is larger than the sum of its proper divisors (321892).

643778 is a wasteful number, since it uses less digits than its factorization.

643778 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 321891.

The product of its digits is 28224, while the sum is 35.

The square root of 643778 is about 802.3577755590. The cubic root of 643778 is about 86.3466269868.

The spelling of 643778 in words is "six hundred forty-three thousand, seven hundred seventy-eight".