305561 has 4 divisors (see below), whose sum is σ = 310800. Its totient is φ = 300324.

The previous prime is 305551. The next prime is 305563. The reversal of 305561 is 165503.

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 305561 - 2⁶ = 305497 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (305563) 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, 2531 + ... + 2648.

It is an arithmetic number, because the mean of its divisors is an integer number (77700).

2³⁰⁵⁵⁶¹ is an apocalyptic number.

It is an amenable number.

305561 is a deficient number, since it is larger than the sum of its proper divisors (5239).

305561 is an equidigital number, since it uses as much as digits as its factorization.

305561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5238.

The product of its (nonzero) digits is 450, while the sum is 20.

The square root of 305561 is about 552.7757230559. The cubic root of 305561 is about 67.3544003833.

It can be divided in two parts, 3055 and 61, that multiplied together give a triangular number (186355 = T₆₁₀).

The spelling of 305561 in words is "three hundred five thousand, five hundred sixty-one".