261881568 has 144 divisors (see below), whose sum is σ = 810416880. Its totient is φ = 79736832.

The previous prime is 261881563. The next prime is 261881591. The reversal of 261881568 is 865188162.

261881568 is a `hidden beast` number, since 2 + 6 + 1 + 8 + 81 + 568 = 666.

It is a tau number, because it is divible by the number of its divisors (144).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (261881561) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 422763 + ... + 423381.

It is an arithmetic number, because the mean of its divisors is an integer number (5627895).

Almost surely, 2^261881568 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 261881568, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (405208440).

261881568 is an abundant number, since it is smaller than the sum of its proper divisors (548535312).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

261881568 is a wasteful number, since it uses less digits than its factorization.

261881568 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 761 (or 750 counting only the distinct ones).

The product of its digits is 184320, while the sum is 45.

The square root of 261881568 is about 16182.7552660232. The cubic root of 261881568 is about 639.7863609846.

The spelling of 261881568 in words is "two hundred sixty-one million, eight hundred eighty-one thousand, five hundred sixty-eight".