18331981 has 2 divisors, whose sum is σ = 18331982. Its totient is φ = 18331980.

The previous prime is 18331969. The next prime is 18331993. The reversal of 18331981 is 18913381.

It is a happy number.

It is a balanced prime because it is at equal distance from previous prime (18331969) and next prime (18331993).

It can be written as a sum of positive squares in only one way, i.e., 18198756 + 133225 = 4266^2 + 365^2 .

It is an emirp because it is prime and its reverse (18913381) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 18331981 - 2¹¹ = 18329933 is a prime.

It is a super-2 number, since 2×18331981² = 672123054768722, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18331381) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9165990 + 9165991.

It is an arithmetic number, because the mean of its divisors is an integer number (9165991).

Almost surely, 2^18331981 is an apocalyptic number.

It is an amenable number.

18331981 is a deficient number, since it is larger than the sum of its proper divisors (1).

18331981 is an equidigital number, since it uses as much as digits as its factorization.

18331981 is an evil number, because the sum of its binary digits is even.

The product of its digits is 5184, while the sum is 34.

The square root of 18331981 is about 4281.5862714653. The cubic root of 18331981 is about 263.6755129085.

The spelling of 18331981 in words is "eighteen million, three hundred thirty-one thousand, nine hundred eighty-one".