221770721 has 2 divisors, whose sum is σ = 221770722. Its totient is φ = 221770720.

The previous prime is 221770693. The next prime is 221770723. The reversal of 221770721 is 127077122.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 194323600 + 27447121 = 13940^2 + 5239^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-221770721 is a prime.

Together with 221770723, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (221770723) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 110885360 + 110885361.

It is an arithmetic number, because the mean of its divisors is an integer number (110885361).

Almost surely, 2^221770721 is an apocalyptic number.

It is an amenable number.

221770721 is a deficient number, since it is larger than the sum of its proper divisors (1).

221770721 is an equidigital number, since it uses as much as digits as its factorization.

221770721 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 2744, while the sum is 29.

The square root of 221770721 is about 14891.9683386717. The cubic root of 221770721 is about 605.2963700595.

The spelling of 221770721 in words is "two hundred twenty-one million, seven hundred seventy thousand, seven hundred twenty-one".