18785581 has 2 divisors, whose sum is σ = 18785582. Its totient is φ = 18785580.

The previous prime is 18785579. The next prime is 18785609. The reversal of 18785581 is 18558781.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 18783556 + 2025 = 4334^2 + 45^2 .

It is a cyclic number.

It is not a de Polignac number, because 18785581 - 2¹ = 18785579 is a prime.

It is a super-2 number, since 2×18785581² = 705796107015122, which contains 22 as substring.

Together with 18785579, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18785681) 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, 9392790 + 9392791.

It is an arithmetic number, because the mean of its divisors is an integer number (9392791).

Almost surely, 2^18785581 is an apocalyptic number.

It is an amenable number.

18785581 is a deficient number, since it is larger than the sum of its proper divisors (1).

18785581 is an equidigital number, since it uses as much as digits as its factorization.

18785581 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 89600, while the sum is 43.

The square root of 18785581 is about 4334.2336116089. The cubic root of 18785581 is about 265.8325825743.

The spelling of 18785581 in words is "eighteen million, seven hundred eighty-five thousand, five hundred eighty-one".