18640813 has 2 divisors, whose sum is σ = 18640814. Its totient is φ = 18640812.

The previous prime is 18640777. The next prime is 18640841. The reversal of 18640813 is 31804681.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 16826404 + 1814409 = 4102^2 + 1347^2 .

It is an emirp because it is prime and its reverse (31804681) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 18640813 - 2¹⁷ = 18509741 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18640883) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9320406 + 9320407.

It is an arithmetic number, because the mean of its divisors is an integer number (9320407).

Almost surely, 2^18640813 is an apocalyptic number.

It is an amenable number.

18640813 is a deficient number, since it is larger than the sum of its proper divisors (1).

18640813 is an equidigital number, since it uses as much as digits as its factorization.

18640813 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 4608, while the sum is 31.

The square root of 18640813 is about 4317.5007817023. The cubic root of 18640813 is about 265.1479558252.

The spelling of 18640813 in words is "eighteen million, six hundred forty thousand, eight hundred thirteen".