17819981 has 2 divisors, whose sum is σ = 17819982. Its totient is φ = 17819980.

The previous prime is 17819959. The next prime is 17819983. The reversal of 17819981 is 18991871.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 14364100 + 3455881 = 3790^2 + 1859^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-17819981 is a prime.

It is a super-2 number, since 2×17819981² = 635103445680722, which contains 22 as substring.

It is a Sophie Germain prime.

Together with 17819983, it forms a pair of twin primes.

It is a Chen prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (17819983) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 8909990 + 8909991.

It is an arithmetic number, because the mean of its divisors is an integer number (8909991).

Almost surely, 2^17819981 is an apocalyptic number.

It is an amenable number.

17819981 is a deficient number, since it is larger than the sum of its proper divisors (1).

17819981 is an equidigital number, since it uses as much as digits as its factorization.

17819981 is an evil number, because the sum of its binary digits is even.

The product of its digits is 36288, while the sum is 44.

The square root of 17819981 is about 4221.3719333885. The cubic root of 17819981 is about 261.1975379040.

The spelling of 17819981 in words is "seventeen million, eight hundred nineteen thousand, nine hundred eighty-one".