123781 has 4 divisors (see below), whose sum is σ = 141472. Its totient is φ = 106092.

The previous prime is 123757. The next prime is 123787. The reversal of 123781 is 187321.

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: 187321 = 19 ⋅9859.

It is not a de Polignac number, because 123781 - 2⁷ = 123653 is a prime.

It is a super-2 number, since 2×123781² = 30643471922, which contains 22 as substring.

It is a Duffinian number.

123781 is a lucky number.

It is a plaindrome in base 13.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (123787) 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, 8835 + ... + 8848.

It is an arithmetic number, because the mean of its divisors is an integer number (35368).

2¹²³⁷⁸¹ is an apocalyptic number.

It is an amenable number.

123781 is a deficient number, since it is larger than the sum of its proper divisors (17691).

123781 is an equidigital number, since it uses as much as digits as its factorization.

123781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 17690.

The product of its digits is 336, while the sum is 22.

The square root of 123781 is about 351.8252407091. The cubic root of 123781 is about 49.8369354438.

The spelling of 123781 in words is "one hundred twenty-three thousand, seven hundred eighty-one".