643544251 has 4 divisors (see below), whose sum is σ = 735479152. Its totient is φ = 551609352.

The previous prime is 643544227. The next prime is 643544263. The reversal of 643544251 is 152445346.

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

It is not a de Polignac number, because 643544251 - 2⁷ = 643544123 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (643544281) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 45967440 + ... + 45967453.

It is an arithmetic number, because the mean of its divisors is an integer number (183869788).

Almost surely, 2^643544251 is an apocalyptic number.

643544251 is a deficient number, since it is larger than the sum of its proper divisors (91934901).

643544251 is an equidigital number, since it uses as much as digits as its factorization.

643544251 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 91934900.

The product of its digits is 57600, while the sum is 34.

The square root of 643544251 is about 25368.1739784321. The cubic root of 643544251 is about 863.3617520530.

Adding to 643544251 its reverse (152445346), we get a palindrome (795989597).

The spelling of 643544251 in words is "six hundred forty-three million, five hundred forty-four thousand, two hundred fifty-one".