18515681 has 2 divisors, whose sum is σ = 18515682. Its totient is φ = 18515680.

The previous prime is 18515677. The next prime is 18515699. The reversal of 18515681 is 18651581.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17808400 + 707281 = 4220^2 + 841^2 .

It is a cyclic number.

It is not a de Polignac number, because 18515681 - 2² = 18515677 is a prime.

It is a super-2 number, since 2×18515681² = 685660885787522, which contains 22 as substring.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (18515881) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9257840 + 9257841.

It is an arithmetic number, because the mean of its divisors is an integer number (9257841).

Almost surely, 2^18515681 is an apocalyptic number.

It is an amenable number.

18515681 is a deficient number, since it is larger than the sum of its proper divisors (1).

18515681 is an equidigital number, since it uses as much as digits as its factorization.

18515681 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 9600, while the sum is 35.

The square root of 18515681 is about 4302.9851266301. The cubic root of 18515681 is about 264.5533284648.

The spelling of 18515681 in words is "eighteen million, five hundred fifteen thousand, six hundred eighty-one".