991309973 has 2 divisors, whose sum is σ = 991309974. Its totient is φ = 991309972.

The previous prime is 991309961. The next prime is 991309981. The reversal of 991309973 is 379903199.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 666517489 + 324792484 = 25817^2 + 18022^2 .

It is a cyclic number.

It is not a de Polignac number, because 991309973 - 2¹⁰ = 991308949 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (991309903) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495654986 + 495654987.

It is an arithmetic number, because the mean of its divisors is an integer number (495654987).

Almost surely, 2^991309973 is an apocalyptic number.

It is an amenable number.

991309973 is a deficient number, since it is larger than the sum of its proper divisors (1).

991309973 is an equidigital number, since it uses as much as digits as its factorization.

991309973 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 413343, while the sum is 50.

The square root of 991309973 is about 31485.0754008943. The cubic root of 991309973 is about 997.0948928585.

The spelling of 991309973 in words is "nine hundred ninety-one million, three hundred nine thousand, nine hundred seventy-three".