18655981 has 2 divisors, whose sum is σ = 18655982. Its totient is φ = 18655980.

The previous prime is 18655979. The next prime is 18655991. The reversal of 18655981 is 18955681.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 14182756 + 4473225 = 3766^2 + 2115^2 .

It is an emirp because it is prime and its reverse (18955681) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 18655981 - 2¹ = 18655979 is a prime.

It is a super-2 number, since 2×18655981² = 696091254144722, which contains 22 as substring.

Together with 18655979, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18655951) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9327990 + 9327991.

It is an arithmetic number, because the mean of its divisors is an integer number (9327991).

Almost surely, 2^18655981 is an apocalyptic number.

It is an amenable number.

18655981 is a deficient number, since it is larger than the sum of its proper divisors (1).

18655981 is an equidigital number, since it uses as much as digits as its factorization.

18655981 is an evil number, because the sum of its binary digits is even.

The product of its digits is 86400, while the sum is 43.

The square root of 18655981 is about 4319.2569962900. The cubic root of 18655981 is about 265.2198531516.

The spelling of 18655981 in words is "eighteen million, six hundred fifty-five thousand, nine hundred eighty-one".