261645840 has 60 divisors (see below), whose sum is σ = 878696364. Its totient is φ = 69772032.

The previous prime is 261645829. The next prime is 261645847. The reversal of 261645840 is 48546162.

261645840 is a `hidden beast` number, since 2 + 6 + 1 + 645 + 8 + 4 + 0 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 50466816 + 211179024 = 7104^2 + 14532^2 .

It is a tau number, because it is divible by the number of its divisors (60).

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a nialpdrome in base 16.

It is a junction number, because it is equal to n+sod(n) for n = 261645795 and 261645804.

It is not an unprimeable number, because it can be changed into a prime (261645847) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 180979 + ... + 182418.

Almost surely, 2^261645840 is an apocalyptic number.

261645840 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

261645840 is an abundant number, since it is smaller than the sum of its proper divisors (617050524).

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

261645840 is a wasteful number, since it uses less digits than its factorization.

261645840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 363416 (or 363407 counting only the distinct ones).

The product of its (nonzero) digits is 46080, while the sum is 36.

The square root of 261645840 is about 16175.4703177373. The cubic root of 261645840 is about 639.5943392825.

The spelling of 261645840 in words is "two hundred sixty-one million, six hundred forty-five thousand, eight hundred forty".