861561 has 12 divisors (see below), whose sum is σ = 1287780. Its totient is φ = 554400.

The previous prime is 861559. The next prime is 861563. The reversal of 861561 is 165168.

It is an interprime number because it is at equal distance from previous prime (861559) and next prime (861563).

It can be written as a sum of positive squares in 2 ways, for example, as 308025 + 553536 = 555^2 + 744^2 .

It is not a de Polignac number, because 861561 - 2¹ = 861559 is a prime.

861561 is a lucky number.

It is not an unprimeable number, because it can be changed into a prime (861563) 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 11 ways as a sum of consecutive naturals, for example, 1390 + ... + 1911.

It is an arithmetic number, because the mean of its divisors is an integer number (107315).

2⁸⁶¹⁵⁶¹ is an apocalyptic number.

It is an amenable number.

861561 is a deficient number, since it is larger than the sum of its proper divisors (426219).

861561 is a wasteful number, since it uses less digits than its factorization.

861561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3336 (or 3333 counting only the distinct ones).

The product of its digits is 1440, while the sum is 27.

The square root of 861561 is about 928.2031027744. The cubic root of 861561 is about 95.1543566360.

The spelling of 861561 in words is "eight hundred sixty-one thousand, five hundred sixty-one".