213981 has 4 divisors (see below), whose sum is σ = 285312. Its totient is φ = 142652.

The previous prime is 213977. The next prime is 213989. The reversal of 213981 is 189312.

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 a cyclic number.

It is not a de Polignac number, because 213981 - 2² = 213977 is a prime.

It is a super-2 number, since 2×213981² = 91575736722, which contains 22 as substring.

It is a D-number.

213981 is a lucky number.

It is a nialpdrome in base 13.

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 213981.

It is not an unprimeable number, because it can be changed into a prime (213989) 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, 35661 + ... + 35666.

It is an arithmetic number, because the mean of its divisors is an integer number (71328).

2²¹³⁹⁸¹ is an apocalyptic number.

It is an amenable number.

213981 is a deficient number, since it is larger than the sum of its proper divisors (71331).

213981 is an equidigital number, since it uses as much as digits as its factorization.

213981 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 71330.

The product of its digits is 432, while the sum is 24.

The square root of 213981 is about 462.5808037522. The cubic root of 213981 is about 59.8124700414.

The spelling of 213981 in words is "two hundred thirteen thousand, nine hundred eighty-one".