181663981 has 2 divisors, whose sum is σ = 181663982. Its totient is φ = 181663980.

The previous prime is 181663967. The next prime is 181663991. The reversal of 181663981 is 189366181.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 91584900 + 90079081 = 9570^2 + 9491^2 .

It is a cyclic number.

It is not a de Polignac number, because 181663981 - 2¹⁷ = 181532909 is a prime.

It is a super-2 number, since 2×181663981² = 66003603985536722, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (181663961) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 90831990 + 90831991.

It is an arithmetic number, because the mean of its divisors is an integer number (90831991).

Almost surely, 2^181663981 is an apocalyptic number.

It is an amenable number.

181663981 is a deficient number, since it is larger than the sum of its proper divisors (1).

181663981 is an equidigital number, since it uses as much as digits as its factorization.

181663981 is an evil number, because the sum of its binary digits is even.

The product of its digits is 62208, while the sum is 43.

The square root of 181663981 is about 13478.2781170296. The cubic root of 181663981 is about 566.3561346276.

The spelling of 181663981 in words is "one hundred eighty-one million, six hundred sixty-three thousand, nine hundred eighty-one".