81800221 has 2 divisors, whose sum is σ = 81800222. Its totient is φ = 81800220.

The previous prime is 81800119. The next prime is 81800281. The reversal of 81800221 is 12200818.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 78960996 + 2839225 = 8886^2 + 1685^2 .

It is a cyclic number.

It is not a de Polignac number, because 81800221 - 2⁷ = 81800093 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 81800192 and 81800201.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81800281) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40900110 + 40900111.

It is an arithmetic number, because the mean of its divisors is an integer number (40900111).

Almost surely, 2^81800221 is an apocalyptic number.

It is an amenable number.

81800221 is a deficient number, since it is larger than the sum of its proper divisors (1).

81800221 is an equidigital number, since it uses as much as digits as its factorization.

81800221 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 256, while the sum is 22.

The square root of 81800221 is about 9044.3474612600. The cubic root of 81800221 is about 434.0950420802.

The spelling of 81800221 in words is "eighty-one million, eight hundred thousand, two hundred twenty-one".