261811578 has 64 divisors (see below), whose sum is σ = 608348160. Its totient is φ = 73576512.

The previous prime is 261811549. The next prime is 261811579. The reversal of 261811578 is 875118162.

It is not an unprimeable number, because it can be changed into a prime (261811579) 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 31 ways as a sum of consecutive naturals, for example, 1143168 + ... + 1143396.

It is an arithmetic number, because the mean of its divisors is an integer number (9505440).

Almost surely, 2^261811578 is an apocalyptic number.

261811578 is an abundant number, since it is smaller than the sum of its proper divisors (346536582).

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

261811578 is a wasteful number, since it uses less digits than its factorization.

261811578 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 571.

The product of its digits is 26880, while the sum is 39.

The square root of 261811578 is about 16180.5926343877. The cubic root of 261811578 is about 639.7293598530.

It can be divided in two parts, 2618 and 11578, that added together give a triangular number (14196 = T₁₆₈).

The spelling of 261811578 in words is "two hundred sixty-one million, eight hundred eleven thousand, five hundred seventy-eight".