18936781 has 2 divisors, whose sum is σ = 18936782. Its totient is φ = 18936780.

The previous prime is 18936773. The next prime is 18936791. The reversal of 18936781 is 18763981.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17926756 + 1010025 = 4234^2 + 1005^2 .

It is an emirp because it is prime and its reverse (18763981) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 18936781 - 2³ = 18936773 is a prime.

It is a super-2 number, since 2×18936781² = 717203349283922, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18936721) 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, 9468390 + 9468391.

It is an arithmetic number, because the mean of its divisors is an integer number (9468391).

Almost surely, 2^18936781 is an apocalyptic number.

It is an amenable number.

18936781 is a deficient number, since it is larger than the sum of its proper divisors (1).

18936781 is an equidigital number, since it uses as much as digits as its factorization.

18936781 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 72576, while the sum is 43.

The square root of 18936781 is about 4351.6411846567. The cubic root of 18936781 is about 266.5438821888.

The spelling of 18936781 in words is "eighteen million, nine hundred thirty-six thousand, seven hundred eighty-one".