17921 has 2 divisors, whose sum is σ = 17922. Its totient is φ = 17920.

The previous prime is 17911. The next prime is 17923. The reversal of 17921 is 12971.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 10000 + 7921 = 100^2 + 89^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-17921 is a prime.

Together with 17923, it forms a pair of twin primes.

It is a Chen prime.

It is a junction number, because it is equal to n+sod(n) for n = 17893 and 17902.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 17921.

It is not a weakly prime, because it can be changed into another prime (17923) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 8960 + 8961.

It is an arithmetic number, because the mean of its divisors is an integer number (8961).

It is a Proth number, since it is equal to 35 ⋅ 2⁹ + 1 and 35 < 2⁹.

2¹⁷⁹²¹ is an apocalyptic number.

It is an amenable number.

17921 is a deficient number, since it is larger than the sum of its proper divisors (1).

17921 is an equidigital number, since it uses as much as digits as its factorization.

17921 is an evil number, because the sum of its binary digits is even.

The product of its digits is 126, while the sum is 20.

The square root of 17921 is about 133.8693392827. The cubic root of 17921 is about 26.1690172383.

Subtracting from 17921 its reverse (12971), we obtain a triangular number (4950 = T₉₉).

The spelling of 17921 in words is "seventeen thousand, nine hundred twenty-one".