23981 has 2 divisors, whose sum is σ = 23982. Its totient is φ = 23980.

The previous prime is 23977. The next prime is 23993. The reversal of 23981 is 18932.

23981 = 109² + 110².

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 12100 + 11881 = 110^2 + 109^2 .

It is a cyclic number.

It is not a de Polignac number, because 23981 - 2² = 23977 is a prime.

It is a super-2 number, since 2×23981² = 1150176722, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Chen prime.

It is an Ulam number.

It is a Curzon number.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 23981.

It is not a weakly prime, because it can be changed into another prime (23911) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 11990 + 11991.

It is an arithmetic number, because the mean of its divisors is an integer number (11991).

2²³⁹⁸¹ is an apocalyptic number.

23981 is the 110-th centered square number.

It is an amenable number.

23981 is a deficient number, since it is larger than the sum of its proper divisors (1).

23981 is an equidigital number, since it uses as much as digits as its factorization.

23981 is an evil number, because the sum of its binary digits is even.

The product of its digits is 432, while the sum is 23.

The square root of 23981 is about 154.8579994705. The cubic root of 23981 is about 28.8373775238.

The spelling of 23981 in words is "twenty-three thousand, nine hundred eighty-one".