Search a number
BaseRepresentation
bin10011111100111001
311011002201
4103330321
510103341
61430201
7460153
oct237471
9134081
1081721
1156442
123b361
132b273
1519331
hex13f39

81721 has 4 divisors (see below), whose sum is σ = 82944. Its totient is φ = 80500.

The previous prime is 81707. The next prime is 81727. The reversal of 81721 is 12718.

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, and also an emirpimes, since its reverse is a distinct semiprime: 12718 = 26359.

It is a cyclic number.

It is not a de Polignac number, because 81721 - 25 = 81689 is a prime.

It is a Duffinian number.

81721 is a lucky number.

It is not an unprimeable number, because it can be changed into a prime (81727) 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 3 ways as a sum of consecutive naturals, for example, 505 + ... + 646.

It is an arithmetic number, because the mean of its divisors is an integer number (20736).

281721 is an apocalyptic number.

It is an amenable number.

81721 is a deficient number, since it is larger than the sum of its proper divisors (1223).

81721 is a wasteful number, since it uses less digits than its factorization.

81721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1222.

The product of its digits is 112, while the sum is 19.

The square root of 81721 is about 285.8688510489. The cubic root of 81721 is about 43.3954860914.

It can be divided in two parts, 817 and 21, that added together give a palindrome (838).

The spelling of 81721 in words is "eighty-one thousand, seven hundred twenty-one".

Divisors: 1 71 1151 81721