18505381 has 2 divisors, whose sum is σ = 18505382. Its totient is φ = 18505380.

The previous prime is 18505307. The next prime is 18505397. The reversal of 18505381 is 18350581.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17564481 + 940900 = 4191^2 + 970^2 .

It is an emirp because it is prime and its reverse (18350581) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 18505381 - 2⁹ = 18504869 is a prime.

It is a super-2 number, since 2×18505381² = 684898251910322, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18505181) 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, 9252690 + 9252691.

It is an arithmetic number, because the mean of its divisors is an integer number (9252691).

Almost surely, 2^18505381 is an apocalyptic number.

It is an amenable number.

18505381 is a deficient number, since it is larger than the sum of its proper divisors (1).

18505381 is an equidigital number, since it uses as much as digits as its factorization.

18505381 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 4800, while the sum is 31.

The square root of 18505381 is about 4301.7881165859. The cubic root of 18505381 is about 264.5042636620.

Subtracting from 18505381 its product of nonzero digits (4800), we obtain a palindrome (18500581).

The spelling of 18505381 in words is "eighteen million, five hundred five thousand, three hundred eighty-one".