18520781 has 2 divisors, whose sum is σ = 18520782. Its totient is φ = 18520780.

The previous prime is 18520771. The next prime is 18520783. The reversal of 18520781 is 18702581.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 10023556 + 8497225 = 3166^2 + 2915^2 .

It is a cyclic number.

It is not a de Polignac number, because 18520781 - 2⁶ = 18520717 is a prime.

It is a super-2 number, since 2×18520781² = 686038657699922, which contains 22 as substring.

Together with 18520783, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18520783) 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, 9260390 + 9260391.

It is an arithmetic number, because the mean of its divisors is an integer number (9260391).

Almost surely, 2^18520781 is an apocalyptic number.

It is an amenable number.

18520781 is a deficient number, since it is larger than the sum of its proper divisors (1).

18520781 is an equidigital number, since it uses as much as digits as its factorization.

18520781 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 4480, while the sum is 32.

The square root of 18520781 is about 4303.5776976836. The cubic root of 18520781 is about 264.5776159524.

The spelling of 18520781 in words is "eighteen million, five hundred twenty thousand, seven hundred eighty-one".