643537881 has 24 divisors (see below), whose sum is σ = 1078211264. Its totient is φ = 362244960.

The previous prime is 643537877. The next prime is 643537901. The reversal of 643537881 is 188735346.

It is not a de Polignac number, because 643537881 - 2² = 643537877 is a prime.

It is a super-2 number, since 2×643537881² = 828282008563940322, which contains 22 as substring.

It is a Smith number, since the sum of its digits (45) coincides with the sum of the digits of its prime factors.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (643537801) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 72010 + ... + 80451.

Almost surely, 2^643537881 is an apocalyptic number.

It is an amenable number.

643537881 is a deficient number, since it is larger than the sum of its proper divisors (434673383).

643537881 is a wasteful number, since it uses less digits than its factorization.

643537881 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 152541 (or 152538 counting only the distinct ones).

The product of its digits is 483840, while the sum is 45.

The square root of 643537881 is about 25368.0484271061. The cubic root of 643537881 is about 863.3589034364.

The spelling of 643537881 in words is "six hundred forty-three million, five hundred thirty-seven thousand, eight hundred eighty-one".