18533981 has 2 divisors, whose sum is σ = 18533982. Its totient is φ = 18533980.

The previous prime is 18533959. The next prime is 18533993. The reversal of 18533981 is 18933581.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 10176100 + 8357881 = 3190^2 + 2891^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-18533981 is a prime.

It is a super-2 number, since 2×18533981² = 687016903416722, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18532981) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9266990 + 9266991.

It is an arithmetic number, because the mean of its divisors is an integer number (9266991).

Almost surely, 2^18533981 is an apocalyptic number.

It is an amenable number.

18533981 is a deficient number, since it is larger than the sum of its proper divisors (1).

18533981 is an equidigital number, since it uses as much as digits as its factorization.

18533981 is an evil number, because the sum of its binary digits is even.

The product of its digits is 25920, while the sum is 38.

The square root of 18533981 is about 4305.1110322499. Note that the first 3 decimals coincide. The cubic root of 18533981 is about 264.6404569877.

The spelling of 18533981 in words is "eighteen million, five hundred thirty-three thousand, nine hundred eighty-one".