261811 has 4 divisors (see below), whose sum is σ = 285624. Its totient is φ = 238000.

The previous prime is 261799. The next prime is 261823. The reversal of 261811 is 118162.

It is a semiprime because it is the product of two primes.

It is an interprime number because it is at equal distance from previous prime (261799) and next prime (261823).

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-261811 is a prime.

It is an Ulam number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (261881) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 11890 + ... + 11911.

It is an arithmetic number, because the mean of its divisors is an integer number (71406).

2²⁶¹⁸¹¹ is an apocalyptic number.

261811 is a deficient number, since it is larger than the sum of its proper divisors (23813).

261811 is a wasteful number, since it uses less digits than its factorization.

261811 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 23812.

The product of its digits is 96, while the sum is 19.

The square root of 261811 is about 511.6747013484. The cubic root of 261811 is about 63.9728889077.

Adding to 261811 its reverse (118162), we get a palindrome (379973).

The spelling of 261811 in words is "two hundred sixty-one thousand, eight hundred eleven".