18918921 has 16 divisors (see below), whose sum is σ = 29010944. Its totient is φ = 10742544.

The previous prime is 18918919. The next prime is 18918923. The reversal of 18918921 is 12981981.

18918921 = T₃₉₈ + T₃₉₉ + ... + T₅₆₀.

It is an interprime number because it is at equal distance from previous prime (18918919) and next prime (18918923).

It is not a de Polignac number, because 18918921 - 2¹ = 18918919 is a prime.

It is a Smith number, since the sum of its digits (39) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 18918921.

It is not an unprimeable number, because it can be changed into a prime (18918923) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 660 + ... + 6186.

It is an arithmetic number, because the mean of its divisors is an integer number (1813184).

Almost surely, 2^18918921 is an apocalyptic number.

It is an amenable number.

18918921 is a deficient number, since it is larger than the sum of its proper divisors (10092023).

18918921 is a wasteful number, since it uses less digits than its factorization.

18918921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5700.

The product of its digits is 10368, while the sum is 39.

The square root of 18918921 is about 4349.5886012358. The cubic root of 18918921 is about 266.4600599328.

It can be divided in two parts, 189 and 18921, that added together give a triangular number (19110 = T₁₉₅).

The spelling of 18918921 in words is "eighteen million, nine hundred eighteen thousand, nine hundred twenty-one".