18817993 has 2 divisors, whose sum is σ = 18817994. Its totient is φ = 18817992.

The previous prime is 18817987. The next prime is 18818029. The reversal of 18817993 is 39971881.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 15904144 + 2913849 = 3988^2 + 1707^2 .

It is a cyclic number.

It is not a de Polignac number, because 18817993 - 2⁹ = 18817481 is a prime.

It is not a weakly prime, because it can be changed into another prime (18817943) 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, 9408996 + 9408997.

It is an arithmetic number, because the mean of its divisors is an integer number (9408997).

Almost surely, 2^18817993 is an apocalyptic number.

It is an amenable number.

18817993 is a deficient number, since it is larger than the sum of its proper divisors (1).

18817993 is an equidigital number, since it uses as much as digits as its factorization.

18817993 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 108864, while the sum is 46.

The square root of 18817993 is about 4337.9710695209. The cubic root of 18817993 is about 265.9853808839.

It can be divided in two parts, 188 and 17993, that added together give a palindrome (18181).

The spelling of 18817993 in words is "eighteen million, eight hundred seventeen thousand, nine hundred ninety-three".