72781 has 4 divisors (see below), whose sum is σ = 73852. Its totient is φ = 71712.

The previous prime is 72767. The next prime is 72797. The reversal of 72781 is 18727.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 18727 = 61 ⋅307.

It can be written as a sum of positive squares in 2 ways, for example, as 52900 + 19881 = 230^2 + 141^2 .

It is a cyclic number.

It is not a de Polignac number, because 72781 - 2⁹ = 72269 is a prime.

It is a super-2 number, since 2×72781² = 10594147922, which contains 22 as substring.

It is an alternating number because its digits alternate between odd and even.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (72701) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 426 + ... + 571.

It is an arithmetic number, because the mean of its divisors is an integer number (18463).

2⁷²⁷⁸¹ is an apocalyptic number.

It is an amenable number.

72781 is a deficient number, since it is larger than the sum of its proper divisors (1071).

72781 is an equidigital number, since it uses as much as digits as its factorization.

It is an anagram of its base 13 representation: 72781 = (27187)₁₃.

72781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1070.

The product of its digits is 784, while the sum is 25.

The square root of 72781 is about 269.7795396245. The cubic root of 72781 is about 41.7515567087.

It can be divided in two parts, 727 and 81, that added together give a palindrome (808).

The spelling of 72781 in words is "seventy-two thousand, seven hundred eighty-one".