131209561 has 4 divisors (see below), whose sum is σ = 149953792. Its totient is φ = 112465332.

The previous prime is 131209541. The next prime is 131209567. The reversal of 131209561 is 165902131.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 165902131 = 2161 ⋅76771.

It is not a de Polignac number, because 131209561 - 2⁹ = 131209049 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (131209567) 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, 9372105 + ... + 9372118.

It is an arithmetic number, because the mean of its divisors is an integer number (37488448).

Almost surely, 2^131209561 is an apocalyptic number.

It is an amenable number.

131209561 is a deficient number, since it is larger than the sum of its proper divisors (18744231).

131209561 is an equidigital number, since it uses as much as digits as its factorization.

131209561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 18744230.

The product of its (nonzero) digits is 1620, while the sum is 28.

The square root of 131209561 is about 11454.6741987714. The cubic root of 131209561 is about 508.1459799639.

The spelling of 131209561 in words is "one hundred thirty-one million, two hundred nine thousand, five hundred sixty-one".