18108721 has 2 divisors, whose sum is σ = 18108722. Its totient is φ = 18108720.

The previous prime is 18108709. The next prime is 18108733. The reversal of 18108721 is 12780181.

It is a balanced prime because it is at equal distance from previous prime (18108709) and next prime (18108733).

It can be written as a sum of positive squares in only one way, i.e., 10491121 + 7617600 = 3239^2 + 2760^2 .

It is an emirp because it is prime and its reverse (12780181) is a distict prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-18108721 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 18108721.

It is not a weakly prime, because it can be changed into another prime (18108421) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9054360 + 9054361.

It is an arithmetic number, because the mean of its divisors is an integer number (9054361).

Almost surely, 2^18108721 is an apocalyptic number.

It is an amenable number.

18108721 is a deficient number, since it is larger than the sum of its proper divisors (1).

18108721 is an equidigital number, since it uses as much as digits as its factorization.

18108721 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 896, while the sum is 28.

The square root of 18108721 is about 4255.4342904103. The cubic root of 18108721 is about 262.6007280853.

The spelling of 18108721 in words is "eighteen million, one hundred eight thousand, seven hundred twenty-one".