18721081 has 4 divisors (see below), whose sum is σ = 18749412. Its totient is φ = 18692752.

The previous prime is 18721033. The next prime is 18721091. The reversal of 18721081 is 18012781.

18721081 = 3059² + 3060².

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 18012781 = 3313 ⋅5437.

It can be written as a sum of positive squares in 2 ways, for example, as 9357481 + 9363600 = 3059^2 + 3060^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-18721081 is a prime.

It is a super-2 number, since 2×18721081² = 700957747617122, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (18721091) 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 in 3 ways as a sum of consecutive naturals, for example, 13150 + ... + 14503.

It is an arithmetic number, because the mean of its divisors is an integer number (4687353).

Almost surely, 2^18721081 is an apocalyptic number.

18721081 is the 3060-th centered square number and also the 2737-th centered pentagonal number.

It is an amenable number.

18721081 is a deficient number, since it is larger than the sum of its proper divisors (28331).

18721081 is an equidigital number, since it uses as much as digits as its factorization.

18721081 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 28330.

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

The square root of 18721081 is about 4326.7864518601. The cubic root of 18721081 is about 265.5279896912.

The spelling of 18721081 in words is "eighteen million, seven hundred twenty-one thousand, eighty-one".