261840 has 40 divisors (see below), whose sum is σ = 812448. Its totient is φ = 69760.

The previous prime is 261823. The next prime is 261847. The reversal of 261840 is 48162.

It is a tau number, because it is divible by the number of its divisors (40).

It is a hoax number, since the sum of its digits (21) coincides with the sum of the digits of its distinct prime factors.

It is a nialpdrome in base 8.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (261847) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 306 + ... + 785.

2²⁶¹⁸⁴⁰ is an apocalyptic number.

261840 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

261840 is an abundant number, since it is smaller than the sum of its proper divisors (550608).

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

261840 is a wasteful number, since it uses less digits than its factorization.

261840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1107 (or 1101 counting only the distinct ones).

The product of its (nonzero) digits is 384, while the sum is 21.

The square root of 261840 is about 511.7030388810. The cubic root of 261840 is about 63.9752508473.

The spelling of 261840 in words is "two hundred sixty-one thousand, eight hundred forty".