991247221 has 2 divisors, whose sum is σ = 991247222. Its totient is φ = 991247220.

The previous prime is 991247189. The next prime is 991247239. The reversal of 991247221 is 122742199.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 981568900 + 9678321 = 31330^2 + 3111^2 .

It is an emirp because it is prime and its reverse (122742199) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 991247221 - 2⁵ = 991247189 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (991247281) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495623610 + 495623611.

It is an arithmetic number, because the mean of its divisors is an integer number (495623611).

Almost surely, 2^991247221 is an apocalyptic number.

It is an amenable number.

991247221 is a deficient number, since it is larger than the sum of its proper divisors (1).

991247221 is an equidigital number, since it uses as much as digits as its factorization.

991247221 is an evil number, because the sum of its binary digits is even.

The product of its digits is 18144, while the sum is 37.

The square root of 991247221 is about 31484.0788494757. The cubic root of 991247221 is about 997.0738530154.

The spelling of 991247221 in words is "nine hundred ninety-one million, two hundred forty-seven thousand, two hundred twenty-one".