19918181 has 2 divisors, whose sum is σ = 19918182. Its totient is φ = 19918180.

The previous prime is 19918141. The next prime is 19918187. The reversal of 19918181 is 18181991.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17986081 + 1932100 = 4241^2 + 1390^2 .

It is a cyclic number.

It is not a de Polignac number, because 19918181 - 2⁶ = 19918117 is a prime.

It is a super-2 number, since 2×19918181² = 793467868697522, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (19918187) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9959090 + 9959091.

It is an arithmetic number, because the mean of its divisors is an integer number (9959091).

Almost surely, 2^19918181 is an apocalyptic number.

It is an amenable number.

19918181 is a deficient number, since it is larger than the sum of its proper divisors (1).

19918181 is an equidigital number, since it uses as much as digits as its factorization.

19918181 is an evil number, because the sum of its binary digits is even.

The product of its digits is 5184, while the sum is 38.

The square root of 19918181 is about 4462.9789378844. The cubic root of 19918181 is about 271.0711041937.

The spelling of 19918181 in words is "nineteen million, nine hundred eighteen thousand, one hundred eighty-one".