261537505 has 4 divisors (see below), whose sum is σ = 313845012. Its totient is φ = 209230000.

The previous prime is 261537491. The next prime is 261537509. The reversal of 261537505 is 505735162.

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 152794321 + 108743184 = 12361^2 + 10428^2 .

It is not a de Polignac number, because 261537505 - 2⁵ = 261537473 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (261537509) 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, 26153746 + ... + 26153755.

It is an arithmetic number, because the mean of its divisors is an integer number (78461253).

Almost surely, 2^261537505 is an apocalyptic number.

It is an amenable number.

261537505 is a deficient number, since it is larger than the sum of its proper divisors (52307507).

261537505 is an equidigital number, since it uses as much as digits as its factorization.

261537505 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 52307506.

The product of its (nonzero) digits is 31500, while the sum is 34.

The square root of 261537505 is about 16172.1212275941. The cubic root of 261537505 is about 639.5060519775.

The spelling of 261537505 in words is "two hundred sixty-one million, five hundred thirty-seven thousand, five hundred five".