18017821 has 2 divisors, whose sum is σ = 18017822. Its totient is φ = 18017820.

The previous prime is 18017801. The next prime is 18017843. The reversal of 18017821 is 12871081.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 16892100 + 1125721 = 4110^2 + 1061^2 .

It is an emirp because it is prime and its reverse (12871081) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 18017821 - 2¹⁹ = 17493533 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 18017821.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18017801) 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, 9008910 + 9008911.

It is an arithmetic number, because the mean of its divisors is an integer number (9008911).

Almost surely, 2^18017821 is an apocalyptic number.

It is an amenable number.

18017821 is a deficient number, since it is larger than the sum of its proper divisors (1).

18017821 is an equidigital number, since it uses as much as digits as its factorization.

18017821 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 18017821 is about 4244.7403925329. The cubic root of 18017821 is about 262.1606002127.

The spelling of 18017821 in words is "eighteen million, seventeen thousand, eight hundred twenty-one".