261209161 has 4 divisors (see below), whose sum is σ = 261242500. Its totient is φ = 261175824.

The previous prime is 261209101. The next prime is 261209167. The reversal of 261209161 is 161902162.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 161902162 = 2 ⋅80951081.

It can be written as a sum of positive squares in 2 ways, for example, as 13461561 + 247747600 = 3669^2 + 15740^2 .

It is a cyclic number.

It is not a de Polignac number, because 261209161 - 2¹⁵ = 261176393 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (261209167) 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, 2215 + ... + 22963.

It is an arithmetic number, because the mean of its divisors is an integer number (65310625).

Almost surely, 2^261209161 is an apocalyptic number.

It is an amenable number.

261209161 is a deficient number, since it is larger than the sum of its proper divisors (33339).

261209161 is a wasteful number, since it uses less digits than its factorization.

261209161 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 33338.

The product of its (nonzero) digits is 1296, while the sum is 28.

The square root of 261209161 is about 16161.9664954485. The cubic root of 261209161 is about 639.2383199393.

The spelling of 261209161 in words is "two hundred sixty-one million, two hundred nine thousand, one hundred sixty-one".