221785721 has 2 divisors, whose sum is σ = 221785722. Its totient is φ = 221785720.

The previous prime is 221785709. The next prime is 221785741. The reversal of 221785721 is 127587122.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 126450025 + 95335696 = 11245^2 + 9764^2 .

It is a cyclic number.

It is not a de Polignac number, because 221785721 - 2⁶ = 221785657 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (221785741) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 110892860 + 110892861.

It is an arithmetic number, because the mean of its divisors is an integer number (110892861).

Almost surely, 2^221785721 is an apocalyptic number.

It is an amenable number.

221785721 is a deficient number, since it is larger than the sum of its proper divisors (1).

221785721 is an equidigital number, since it uses as much as digits as its factorization.

221785721 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 15680, while the sum is 35.

The square root of 221785721 is about 14892.4719573347. The cubic root of 221785721 is about 605.3100166473.

The spelling of 221785721 in words is "two hundred twenty-one million, seven hundred eighty-five thousand, seven hundred twenty-one".