216981 has 6 divisors (see below), whose sum is σ = 313430. Its totient is φ = 144648.

The previous prime is 216973. The next prime is 216991. The reversal of 216981 is 189612.

It can be written as a sum of positive squares in only one way, i.e., 194481 + 22500 = 441^2 + 150^2 .

It is not a de Polignac number, because 216981 - 2³ = 216973 is a prime.

It is a super-2 number, since 2×216981² = 94161508722, which contains 22 as substring.

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

It is a Duffinian number.

It is a Curzon number.

It is a plaindrome in base 13 and base 15.

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 216981.

It is not an unprimeable number, because it can be changed into a prime (216901) 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 5 ways as a sum of consecutive naturals, for example, 12046 + ... + 12063.

2²¹⁶⁹⁸¹ is an apocalyptic number.

It is an amenable number.

216981 is a deficient number, since it is larger than the sum of its proper divisors (96449).

216981 is a wasteful number, since it uses less digits than its factorization.

216981 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 24115 (or 24112 counting only the distinct ones).

The product of its digits is 864, while the sum is 27.

The square root of 216981 is about 465.8121939151. The cubic root of 216981 is about 60.0906961677.

The spelling of 216981 in words is "two hundred sixteen thousand, nine hundred eighty-one".