1809221 has 2 divisors, whose sum is σ = 1809222. Its totient is φ = 1809220.

The previous prime is 1809217. The next prime is 1809229. The reversal of 1809221 is 1229081.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1809025 + 196 = 1345^2 + 14^2 .

It is a cyclic number.

It is not a de Polignac number, because 1809221 - 2² = 1809217 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is equal to p₁₃₅₇₁₆ and since 1809221 and 135716 have the same sum of digits, it is a Honaker prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1809229) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 904610 + 904611.

It is an arithmetic number, because the mean of its divisors is an integer number (904611).

2^1809221 is an apocalyptic number.

It is an amenable number.

1809221 is a deficient number, since it is larger than the sum of its proper divisors (1).

1809221 is an equidigital number, since it uses as much as digits as its factorization.

1809221 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 288, while the sum is 23.

The square root of 1809221 is about 1345.0728604801. The cubic root of 1809221 is about 121.8514046805.

The spelling of 1809221 in words is "one million, eight hundred nine thousand, two hundred twenty-one".