81761 has 2 divisors, whose sum is σ = 81762. Its totient is φ = 81760.

The previous prime is 81749. The next prime is 81769. The reversal of 81761 is 16718.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 67600 + 14161 = 260^2 + 119^2 .

It is a cyclic number.

It is not a de Polignac number, because 81761 - 2¹⁰ = 80737 is a prime.

It is a super-2 number, since 2×81761² = 13369722242, which contains 22 as substring.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (81769) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40880 + 40881.

It is an arithmetic number, because the mean of its divisors is an integer number (40881).

2⁸¹⁷⁶¹ is an apocalyptic number.

It is an amenable number.

81761 is a deficient number, since it is larger than the sum of its proper divisors (1).

81761 is an equidigital number, since it uses as much as digits as its factorization.

81761 is an evil number, because the sum of its binary digits is even.

The product of its digits is 336, while the sum is 23.

The square root of 81761 is about 285.9388046418. The cubic root of 81761 is about 43.4025652033.

It can be divided in two parts, 817 and 61, that added together give a palindrome (878).

The spelling of 81761 in words is "eighty-one thousand, seven hundred sixty-one".