643661381 has 8 divisors (see below), whose sum is σ = 717116544. Its totient is φ = 572696320.

The previous prime is 643661377. The next prime is 643661393. The reversal of 643661381 is 183166346.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 643661381 - 2² = 643661377 is a prime.

It is a super-2 number, since 2×643661381² = 828599946781654322, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (643661311) by changing a digit.

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 7 ways as a sum of consecutive naturals, for example, 621980 + ... + 623013.

It is an arithmetic number, because the mean of its divisors is an integer number (89639568).

Almost surely, 2^643661381 is an apocalyptic number.

It is an amenable number.

643661381 is a deficient number, since it is larger than the sum of its proper divisors (73455163).

643661381 is a wasteful number, since it uses less digits than its factorization.

643661381 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1245051.

The product of its digits is 62208, while the sum is 38.

The square root of 643661381 is about 25370.4824747185. The cubic root of 643661381 is about 863.4141283671.

The spelling of 643661381 in words is "six hundred forty-three million, six hundred sixty-one thousand, three hundred eighty-one".