17887981 has 2 divisors, whose sum is σ = 17887982. Its totient is φ = 17887980.

The previous prime is 17887979. The next prime is 17888011. The reversal of 17887981 is 18978871.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17015625 + 872356 = 4125^2 + 934^2 .

It is an emirp because it is prime and its reverse (18978871) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 17887981 - 2¹ = 17887979 is a prime.

It is a super-2 number, since 2×17887981² = 639959728512722, which contains 22 as substring.

Together with 17887979, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (17887901) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 8943990 + 8943991.

It is an arithmetic number, because the mean of its divisors is an integer number (8943991).

Almost surely, 2^17887981 is an apocalyptic number.

It is an amenable number.

17887981 is a deficient number, since it is larger than the sum of its proper divisors (1).

17887981 is an equidigital number, since it uses as much as digits as its factorization.

17887981 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 225792, while the sum is 49.

The square root of 17887981 is about 4229.4185179526. The cubic root of 17887981 is about 261.5293543475.

The spelling of 17887981 in words is "seventeen million, eight hundred eighty-seven thousand, nine hundred eighty-one".