261985 has 8 divisors (see below), whose sum is σ = 317376. Its totient is φ = 207600.

The previous prime is 261983. The next prime is 262007. The reversal of 261985 is 589162.

261985 is nontrivially palindromic in base 13.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 261985 - 2¹ = 261983 is a prime.

It is a super-2 number, since 2×261985² = 137272280450, which contains 22 as substring.

It is a Duffinian number.

261985 is a lucky number.

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 (261983) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 582 + ... + 928.

It is an arithmetic number, because the mean of its divisors is an integer number (39672).

2²⁶¹⁹⁸⁵ is an apocalyptic number.

It is an amenable number.

261985 is a deficient number, since it is larger than the sum of its proper divisors (55391).

261985 is a wasteful number, since it uses less digits than its factorization.

261985 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 503.

The product of its digits is 4320, while the sum is 31.

The square root of 261985 is about 511.8447030106. The cubic root of 261985 is about 63.9870579299.

It can be divided in two parts, 2619 and 85, that added together give a square (2704 = 52²).

The spelling of 261985 in words is "two hundred sixty-one thousand, nine hundred eighty-five".