643778101 has 4 divisors (see below), whose sum is σ = 643893804. Its totient is φ = 643662400.

The previous prime is 643778099. The next prime is 643778111. The reversal of 643778101 is 101877346.

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

It can be written as a sum of positive squares in 2 ways, for example, as 474804100 + 168974001 = 21790^2 + 12999^2 .

It is a cyclic number.

It is not a de Polignac number, because 643778101 - 2¹ = 643778099 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (643778111) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 49060 + ... + 60781.

It is an arithmetic number, because the mean of its divisors is an integer number (160973451).

Almost surely, 2^643778101 is an apocalyptic number.

It is an amenable number.

643778101 is a deficient number, since it is larger than the sum of its proper divisors (115703).

643778101 is a wasteful number, since it uses less digits than its factorization.

643778101 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 115702.

The product of its (nonzero) digits is 28224, while the sum is 37.

The square root of 643778101 is about 25372.7826814482. The cubic root of 643778101 is about 863.4663150236.

The spelling of 643778101 in words is "six hundred forty-three million, seven hundred seventy-eight thousand, one hundred one".