261436561 has 27 divisors (see below), whose sum is σ = 296445051. Its totient is φ = 230505264.

The previous prime is 261436543. The next prime is 261436573. The reversal of 261436561 is 165634162.

261436561 = 204² + 205² + ... + 925².

The square root of 261436561 is 16169.

It is a perfect power (a square), and thus also a powerful number.

261436561 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It can be written as a sum of positive squares in only one way, i.e., 233937025 + 27499536 = 15295^2 + 5244^2 .

It is not a de Polignac number, because 261436561 - 2⁵ = 261436529 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (261436061) by changing a digit.

It is a polite number, since it can be written in 26 ways as a sum of consecutive naturals, for example, 7065835 + ... + 7065871.

Almost surely, 2^261436561 is an apocalyptic number.

261436561 is the 16169-th square number.

261436561 is the 8085-th centered octagonal number.

It is an amenable number.

261436561 is a deficient number, since it is larger than the sum of its proper divisors (35008490).

261436561 is an equidigital number, since it uses as much as digits as its factorization.

261436561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 158 (or 79 counting only the distinct ones).

The product of its digits is 25920, while the sum is 34.

The cubic root of 261436561 is about 639.4237660024.

The spelling of 261436561 in words is "two hundred sixty-one million, four hundred thirty-six thousand, five hundred sixty-one".