643777661 has 8 divisors (see below), whose sum is σ = 653304384. Its totient is φ = 634263840.

The previous prime is 643777657. The next prime is 643777691. The reversal of 643777661 is 166777346.

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 643777661 - 2² = 643777657 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 (643777621) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 149606 + ... + 153848.

It is an arithmetic number, because the mean of its divisors is an integer number (81663048).

Almost surely, 2^643777661 is an apocalyptic number.

It is an amenable number.

643777661 is a deficient number, since it is larger than the sum of its proper divisors (9526723).

643777661 is a wasteful number, since it uses less digits than its factorization.

643777661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6451.

The product of its digits is 889056, while the sum is 47.

The square root of 643777661 is about 25372.7740107384. The cubic root of 643777661 is about 863.4661183071.

The spelling of 643777661 in words is "six hundred forty-three million, seven hundred seventy-seven thousand, six hundred sixty-one".