261505 has 4 divisors (see below), whose sum is σ = 313812. Its totient is φ = 209200.

The previous prime is 261467. The next prime is 261509. The reversal of 261505 is 505162.

It is a happy number.

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

It can be written as a sum of positive squares in 2 ways, for example, as 173889 + 87616 = 417^2 + 296^2 .

It is not a de Polignac number, because 261505 - 2¹⁵ = 228737 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (261509) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 26146 + ... + 26155.

It is an arithmetic number, because the mean of its divisors is an integer number (78453).

2²⁶¹⁵⁰⁵ is an apocalyptic number.

It is an amenable number.

261505 is a deficient number, since it is larger than the sum of its proper divisors (52307).

261505 is an equidigital number, since it uses as much as digits as its factorization.

261505 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 52306.

The product of its (nonzero) digits is 300, while the sum is 19.

The square root of 261505 is about 511.3755958197. The cubic root of 261505 is about 63.9479557364.

Adding to 261505 its reverse (505162), we get a palindrome (766667).

The spelling of 261505 in words is "two hundred sixty-one thousand, five hundred five".