643961691 has 8 divisors (see below), whose sum is σ = 954017360. Its totient is φ = 429307776.

The previous prime is 643961671. The next prime is 643961741. The reversal of 643961691 is 196169346.

It is not a de Polignac number, because 643961691 - 2¹⁴ = 643945307 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (643961611) 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, 11925190 + ... + 11925243.

It is an arithmetic number, because the mean of its divisors is an integer number (119252170).

Almost surely, 2^643961691 is an apocalyptic number.

643961691 is a deficient number, since it is larger than the sum of its proper divisors (310055669).

643961691 is a wasteful number, since it uses less digits than its factorization.

643961691 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 23850442 (or 23850436 counting only the distinct ones).

The product of its digits is 209952, while the sum is 45.

The square root of 643961691 is about 25376.4002766350. The cubic root of 643961691 is about 863.5483871505.

The spelling of 643961691 in words is "six hundred forty-three million, nine hundred sixty-one thousand, six hundred ninety-one".