643551988 has 12 divisors (see below), whose sum is σ = 1126520640. Its totient is φ = 321688952.

The previous prime is 643551947. The next prime is 643552001. The reversal of 643551988 is 889155346.

It is a super-5 number, since 5×643551988⁵ (a number of 45 digits) contains 55555 as substring. Note that it is a super-d number also for d = 2.

It is a congruent number.

It is an unprimeable number.

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 3 ways as a sum of consecutive naturals, for example, 3406 + ... + 36037.

It is an arithmetic number, because the mean of its divisors is an integer number (93876720).

Almost surely, 2^643551988 is an apocalyptic number.

It is an amenable number.

643551988 is a deficient number, since it is larger than the sum of its proper divisors (482968652).

643551988 is a wasteful number, since it uses less digits than its factorization.

643551988 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 43526 (or 43524 counting only the distinct ones).

The product of its digits is 1036800, while the sum is 49.

The square root of 643551988 is about 25368.3264721976. The cubic root of 643551988 is about 863.3652119566.

The spelling of 643551988 in words is "six hundred forty-three million, five hundred fifty-one thousand, nine hundred eighty-eight".