643973491 has 4 divisors (see below), whose sum is σ = 735969712. Its totient is φ = 551977272.

The previous prime is 643973483. The next prime is 643973503. The reversal of 643973491 is 194379346.

It is a semiprime because it is the product of two primes.

It is not a de Polignac number, because 643973491 - 2³ = 643973483 is a prime.

It is a super-3 number, since 3×643973491³ (a number of 27 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (643973411) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 45998100 + ... + 45998113.

It is an arithmetic number, because the mean of its divisors is an integer number (183992428).

Almost surely, 2^643973491 is an apocalyptic number.

643973491 is a deficient number, since it is larger than the sum of its proper divisors (91996221).

643973491 is an equidigital number, since it uses as much as digits as its factorization.

643973491 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 91996220.

The product of its digits is 489888, while the sum is 46.

The square root of 643973491 is about 25376.6327750551. The cubic root of 643973491 is about 863.5536616924.

The spelling of 643973491 in words is "six hundred forty-three million, nine hundred seventy-three thousand, four hundred ninety-one".