643661369 has 8 divisors (see below), whose sum is σ = 696768072. Its totient is φ = 591068160.

The previous prime is 643661357. The next prime is 643661377. The reversal of 643661369 is 963166346.

It can be written as a sum of positive squares in 4 ways, for example, as 16810000 + 626851369 = 4100^2 + 25037^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 643661369 - 2⁴ = 643661353 is a prime.

It is a super-2 number, since 2×643661369² = 828599915885908322, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (643661399) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 125762 + ... + 130779.

It is an arithmetic number, because the mean of its divisors is an integer number (87096009).

Almost surely, 2^643661369 is an apocalyptic number.

It is an amenable number.

643661369 is a deficient number, since it is larger than the sum of its proper divisors (53106703).

643661369 is a wasteful number, since it uses less digits than its factorization.

643661369 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 256747.

The product of its digits is 419904, while the sum is 44.

The square root of 643661369 is about 25370.4822382232. The cubic root of 643661369 is about 863.4141230015.

The spelling of 643661369 in words is "six hundred forty-three million, six hundred sixty-one thousand, three hundred sixty-nine".