18911381 has 2 divisors, whose sum is σ = 18911382. Its totient is φ = 18911380.

The previous prime is 18911377. The next prime is 18911383. The reversal of 18911381 is 18311981.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15171025 + 3740356 = 3895^2 + 1934^2 .

It is a cyclic number.

It is not a de Polignac number, because 18911381 - 2² = 18911377 is a prime.

It is a super-2 number, since 2×18911381² = 715280662654322, which contains 22 as substring.

Together with 18911383, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18911383) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9455690 + 9455691.

It is an arithmetic number, because the mean of its divisors is an integer number (9455691).

Almost surely, 2^18911381 is an apocalyptic number.

It is an amenable number.

18911381 is a deficient number, since it is larger than the sum of its proper divisors (1).

18911381 is an equidigital number, since it uses as much as digits as its factorization.

18911381 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1728, while the sum is 32.

The square root of 18911381 is about 4348.7217662205. The cubic root of 18911381 is about 266.4246566485.

The spelling of 18911381 in words is "eighteen million, nine hundred eleven thousand, three hundred eighty-one".