8181221 has 2 divisors, whose sum is σ = 8181222. Its totient is φ = 8181220.

The previous prime is 8181211. The next prime is 8181253. The reversal of 8181221 is 1221818.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 4456321 + 3724900 = 2111^2 + 1930^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-8181221 is a prime.

It is a Sophie Germain prime.

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 (8181211) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 4090610 + 4090611.

It is an arithmetic number, because the mean of its divisors is an integer number (4090611).

Almost surely, 2^8181221 is an apocalyptic number.

It is an amenable number.

8181221 is a deficient number, since it is larger than the sum of its proper divisors (1).

8181221 is an equidigital number, since it uses as much as digits as its factorization.

8181221 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 256, while the sum is 23.

The square root of 8181221 is about 2860.2833775694. The cubic root of 8181221 is about 201.4989132317.

The spelling of 8181221 in words is "eight million, one hundred eighty-one thousand, two hundred twenty-one".