643440261 has 16 divisors (see below), whose sum is σ = 892274240. Its totient is φ = 412110720.

The previous prime is 643440251. The next prime is 643440271. The reversal of 643440261 is 162044346.

It is an interprime number because it is at equal distance from previous prime (643440251) and next prime (643440271).

It is not a de Polignac number, because 643440261 - 2¹⁵ = 643407493 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (643440241) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 33016 + ... + 48753.

It is an arithmetic number, because the mean of its divisors is an integer number (55767140).

Almost surely, 2^643440261 is an apocalyptic number.

643440261 is a gapful number since it is divisible by the number (61) formed by its first and last digit.

It is an amenable number.

643440261 is a deficient number, since it is larger than the sum of its proper divisors (248833979).

643440261 is a wasteful number, since it uses less digits than its factorization.

643440261 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 81876.

The product of its (nonzero) digits is 13824, while the sum is 30.

The square root of 643440261 is about 25366.1242802285. The cubic root of 643440261 is about 863.3152461472.

The spelling of 643440261 in words is "six hundred forty-three million, four hundred forty thousand, two hundred sixty-one".