643500661 has 4 divisors (see below), whose sum is σ = 647220492. Its totient is φ = 639780832.

The previous prime is 643500659. The next prime is 643500667. The reversal of 643500661 is 166005346.

643500661 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

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 251698225 + 391802436 = 15865^2 + 19794^2 .

It is a cyclic number.

It is not a de Polignac number, because 643500661 - 2¹ = 643500659 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 (643500667) 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, 1859656 + ... + 1860001.

It is an arithmetic number, because the mean of its divisors is an integer number (161805123).

Almost surely, 2^643500661 is an apocalyptic number.

It is an amenable number.

643500661 is a deficient number, since it is larger than the sum of its proper divisors (3719831).

643500661 is a wasteful number, since it uses less digits than its factorization.

643500661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3719830.

The product of its (nonzero) digits is 12960, while the sum is 31.

The square root of 643500661 is about 25367.3148165114. The cubic root of 643500661 is about 863.3422585536.

The spelling of 643500661 in words is "six hundred forty-three million, five hundred thousand, six hundred sixty-one".