17998921 has 2 divisors, whose sum is σ = 17998922. Its totient is φ = 17998920.

The previous prime is 17998919. The next prime is 17998927. The reversal of 17998921 is 12989971.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17943696 + 55225 = 4236^2 + 235^2 .

It is a cyclic number.

It is not a de Polignac number, because 17998921 - 2¹ = 17998919 is a prime.

It is a super-2 number, since 2×17998921² = 647922314328482, which contains 22 as substring.

Together with 17998919, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (17998927) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 8999460 + 8999461.

It is an arithmetic number, because the mean of its divisors is an integer number (8999461).

Almost surely, 2^17998921 is an apocalyptic number.

It is an amenable number.

17998921 is a deficient number, since it is larger than the sum of its proper divisors (1).

17998921 is an equidigital number, since it uses as much as digits as its factorization.

17998921 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 81648, while the sum is 46.

The square root of 17998921 is about 4242.5135238441. The cubic root of 17998921 is about 262.0689026867.

The spelling of 17998921 in words is "seventeen million, nine hundred ninety-eight thousand, nine hundred twenty-one".