77561 has 6 divisors (see below), whose sum is σ = 85386. Its totient is φ = 70400.

The previous prime is 77557. The next prime is 77563. The reversal of 77561 is 16577.

It can be written as a sum of positive squares in only one way, i.e., 75625 + 1936 = 275^2 + 44^2 .

It is not a de Polignac number, because 77561 - 2² = 77557 is a prime.

It is a Duffinian number.

It is a nialpdrome in base 11.

It is a self number, because there is not a number n which added to its sum of digits gives 77561.

It is not an unprimeable number, because it can be changed into a prime (77563) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 200 + ... + 441.

It is an arithmetic number, because the mean of its divisors is an integer number (14231).

2⁷⁷⁵⁶¹ is an apocalyptic number.

It is an amenable number.

77561 is a deficient number, since it is larger than the sum of its proper divisors (7825).

77561 is a wasteful number, since it uses less digits than its factorization.

77561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 663 (or 652 counting only the distinct ones).

The product of its digits is 1470, while the sum is 26.

The square root of 77561 is about 278.4977558258. The cubic root of 77561 is about 42.6462779648.

The spelling of 77561 in words is "seventy-seven thousand, five hundred sixty-one".