16981 has 2 divisors, whose sum is σ = 16982.
Its totient is φ = 16980.
The previous prime is 16979. The next prime is 16987. The reversal of 16981 is 18961.
It is a weak prime.
It can be written as a sum of positive squares in only one way, i.e., 16900 + 81 = 130^2 + 9^2
.It is also a bemirp because it and its reverse can be mirrored producing other two distinct primes, 18691 and 19681.
It is a cyclic number.
It is not a de Polignac number, because 16981 - 21 = 16979 is a prime.
It is a super-2 number, since 2×169812 = 576708722, which contains 22 as substring.
Together with 16979, it forms a pair of twin primes.
It is an alternating number because its digits alternate between odd and even.
16981 is a lucky number.
It is a congruent number.
It is not a weakly prime, because it can be changed into another prime (16987) by changing a digit.
It is a polite number, since it can be written as a sum of consecutive naturals, namely, 8490 + 8491.
It is an arithmetic number, because the mean of its divisors is an integer number (8491).
216981 is an apocalyptic number.
It is an amenable number.
16981 is a deficient number, since it is larger than the sum of its proper divisors (1).
16981 is an equidigital number, since it uses as much as digits as its factorization.
16981 is an evil number, because the sum of its binary digits is even.
The product of its digits is 432, while the sum is 25.
The square root of 16981 is about 130.3111660603.
The cubic root of 16981 is about 25.7032330513.
It can be divided in two parts, 169 and 81, that multiplied together give a square (13689 = 1172).
The spelling of 16981 in words is "sixteen thousand, nine hundred eighty-one".