81561 has 8 divisors (see below), whose sum is σ = 112384. Its totient is φ = 52560.

The previous prime is 81559. The next prime is 81563. The reversal of 81561 is 16518.

It is an interprime number because it is at equal distance from previous prime (81559) and next prime (81563).

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 81561 - 2¹ = 81559 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81563) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 346 + ... + 531.

It is an arithmetic number, because the mean of its divisors is an integer number (14048).

2⁸¹⁵⁶¹ is an apocalyptic number.

It is an amenable number.

81561 is a deficient number, since it is larger than the sum of its proper divisors (30823).

81561 is a wasteful number, since it uses less digits than its factorization.

81561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 911.

The product of its digits is 240, while the sum is 21.

The square root of 81561 is about 285.5888653292. The cubic root of 81561 is about 43.3671465211.

The spelling of 81561 in words is "eighty-one thousand, five hundred sixty-one".