18711221 has 2 divisors, whose sum is σ = 18711222. Its totient is φ = 18711220.

The previous prime is 18711193. The next prime is 18711223. The reversal of 18711221 is 12211781.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18447025 + 264196 = 4295^2 + 514^2 .

It is a cyclic number.

It is not a de Polignac number, because 18711221 - 2²² = 14516917 is a prime.

It is a Sophie Germain prime.

Together with 18711223, it forms a pair of twin primes.

It is a Chen 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 (18711223) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9355610 + 9355611.

It is an arithmetic number, because the mean of its divisors is an integer number (9355611).

Almost surely, 2^18711221 is an apocalyptic number.

It is an amenable number.

18711221 is a deficient number, since it is larger than the sum of its proper divisors (1).

18711221 is an equidigital number, since it uses as much as digits as its factorization.

18711221 is an evil number, because the sum of its binary digits is even.

The product of its digits is 224, while the sum is 23.

The square root of 18711221 is about 4325.6468880388. The cubic root of 18711221 is about 265.4813655006.

The spelling of 18711221 in words is "eighteen million, seven hundred eleven thousand, two hundred twenty-one".