1805505721 has 2 divisors, whose sum is σ = 1805505722. Its totient is φ = 1805505720.

The previous prime is 1805505701. The next prime is 1805505731. The reversal of 1805505721 is 1275055081.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1742144121 + 63361600 = 41739^2 + 7960^2 .

It is a cyclic number.

It is not a de Polignac number, because 1805505721 - 2⁹ = 1805505209 is a prime.

It is not a weakly prime, because it can be changed into another prime (1805505701) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 902752860 + 902752861.

It is an arithmetic number, because the mean of its divisors is an integer number (902752861).

Almost surely, 2^1805505721 is an apocalyptic number.

It is an amenable number.

1805505721 is a deficient number, since it is larger than the sum of its proper divisors (1).

1805505721 is an equidigital number, since it uses as much as digits as its factorization.

1805505721 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 14000, while the sum is 34.

The square root of 1805505721 is about 42491.2428742676. The cubic root of 1805505721 is about 1217.6793925458.

The spelling of 1805505721 in words is "one billion, eight hundred five million, five hundred five thousand, seven hundred twenty-one".