18121997 has 2 divisors, whose sum is σ = 18121998. Its totient is φ = 18121996.

The previous prime is 18121993. The next prime is 18122021. The reversal of 18121997 is 79912181.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 15768841 + 2353156 = 3971^2 + 1534^2 .

It is a cyclic number.

It is not a de Polignac number, because 18121997 - 2² = 18121993 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 18121997.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18121993) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9060998 + 9060999.

It is an arithmetic number, because the mean of its divisors is an integer number (9060999).

Almost surely, 2^18121997 is an apocalyptic number.

It is an amenable number.

18121997 is a deficient number, since it is larger than the sum of its proper divisors (1).

18121997 is an equidigital number, since it uses as much as digits as its factorization.

18121997 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 9072, while the sum is 38.

The square root of 18121997 is about 4256.9938924081. The cubic root of 18121997 is about 262.6648856745.

The spelling of 18121997 in words is "eighteen million, one hundred twenty-one thousand, nine hundred ninety-seven".