261605121 has 4 divisors (see below), whose sum is σ = 348806832. Its totient is φ = 174403412.

The previous prime is 261605119. The next prime is 261605159. The reversal of 261605121 is 121506162.

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.

It is a cyclic number.

It is not a de Polignac number, because 261605121 - 2¹ = 261605119 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 261605091 and 261605100.

It is not an unprimeable number, because it can be changed into a prime (261605101) 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, 43600851 + ... + 43600856.

It is an arithmetic number, because the mean of its divisors is an integer number (87201708).

Almost surely, 2^261605121 is an apocalyptic number.

It is an amenable number.

261605121 is a deficient number, since it is larger than the sum of its proper divisors (87201711).

261605121 is an equidigital number, since it uses as much as digits as its factorization.

261605121 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 87201710.

The product of its (nonzero) digits is 720, while the sum is 24.

The square root of 261605121 is about 16174.2116036609. The cubic root of 261605121 is about 639.5611583065.

It can be divided in two parts, 261605 and 121, that added together give a triangular number (261726 = T₇₂₃).

The spelling of 261605121 in words is "two hundred sixty-one million, six hundred five thousand, one hundred twenty-one".