643777691 has 2 divisors, whose sum is σ = 643777692. Its totient is φ = 643777690.

The previous prime is 643777657. The next prime is 643777711. The reversal of 643777691 is 196777346.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 643777691 - 2¹⁸ = 643515547 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (643777621) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 321888845 + 321888846.

It is an arithmetic number, because the mean of its divisors is an integer number (321888846).

Almost surely, 2^643777691 is an apocalyptic number.

643777691 is a deficient number, since it is larger than the sum of its proper divisors (1).

643777691 is an equidigital number, since it uses as much as digits as its factorization.

643777691 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1333584, while the sum is 50.

The square root of 643777691 is about 25372.7746019232. The cubic root of 643777691 is about 863.4661317196.

The spelling of 643777691 in words is "six hundred forty-three million, seven hundred seventy-seven thousand, six hundred ninety-one".