18641981 has 2 divisors, whose sum is σ = 18641982. Its totient is φ = 18641980.

The previous prime is 18641977. The next prime is 18641989. The reversal of 18641981 is 18914681.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17056900 + 1585081 = 4130^2 + 1259^2 .

It is a cyclic number.

It is not a de Polignac number, because 18641981 - 2² = 18641977 is a prime.

It is a super-2 number, since 2×18641981² = 695046911208722, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18641989) 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, 9320990 + 9320991.

It is an arithmetic number, because the mean of its divisors is an integer number (9320991).

Almost surely, 2^18641981 is an apocalyptic number.

It is an amenable number.

18641981 is a deficient number, since it is larger than the sum of its proper divisors (1).

18641981 is an equidigital number, since it uses as much as digits as its factorization.

18641981 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 13824, while the sum is 38.

The square root of 18641981 is about 4317.6360430217. The cubic root of 18641981 is about 265.1534936084.

The spelling of 18641981 in words is "eighteen million, six hundred forty-one thousand, nine hundred eighty-one".