643139261 has 4 divisors (see below), whose sum is σ = 658096032. Its totient is φ = 628182492.

The previous prime is 643139251. The next prime is 643139269. The reversal of 643139261 is 162931346.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-643139261 is a prime.

It is a super-2 number, since 2×643139261² = 827256218079252242, 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 (643139269) 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, 7478321 + ... + 7478406.

It is an arithmetic number, because the mean of its divisors is an integer number (164524008).

Almost surely, 2^643139261 is an apocalyptic number.

It is an amenable number.

643139261 is a deficient number, since it is larger than the sum of its proper divisors (14956771).

643139261 is a wasteful number, since it uses less digits than its factorization.

643139261 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 14956770.

The product of its digits is 23328, while the sum is 35.

The square root of 643139261 is about 25360.1904764140. The cubic root of 643139261 is about 863.1806061318.

The spelling of 643139261 in words is "six hundred forty-three million, one hundred thirty-nine thousand, two hundred sixty-one".