23781 has 4 divisors (see below), whose sum is σ = 31712. Its totient is φ = 15852.

The previous prime is 23773. The next prime is 23789. The reversal of 23781 is 18732.

23781 is nontrivially palindromic in base 9.

23781 is an esthetic number in base 3, because in such base its adjacent digits differ by 1.

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.

It is an interprime number because it is at equal distance from previous prime (23773) and next prime (23789).

It is not a de Polignac number, because 23781 - 2³ = 23773 is a prime.

It is a super-2 number, since 2×23781² = 1131071922, which contains 22 as substring.

It is a D-number.

It is a Duffinian number.

It is a Curzon number.

23781 is a lucky number.

It is a nialpdrome in base 13.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (23789) 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, 3961 + ... + 3966.

It is an arithmetic number, because the mean of its divisors is an integer number (7928).

2²³⁷⁸¹ is an apocalyptic number.

It is an amenable number.

23781 is a deficient number, since it is larger than the sum of its proper divisors (7931).

23781 is an equidigital number, since it uses as much as digits as its factorization.

23781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7930.

The product of its digits is 336, while the sum is 21.

The square root of 23781 is about 154.2108945568. The cubic root of 23781 is about 28.7569863299.

The spelling of 23781 in words is "twenty-three thousand, seven hundred eighty-one".