1991015321 has 2 divisors, whose sum is σ = 1991015322. Its totient is φ = 1991015320.

The previous prime is 1991015303. The next prime is 1991015347. The reversal of 1991015321 is 1235101991.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1633048921 + 357966400 = 40411^2 + 18920^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1991015321 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (1991015381) 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, 995507660 + 995507661.

It is an arithmetic number, because the mean of its divisors is an integer number (995507661).

Almost surely, 2^1991015321 is an apocalyptic number.

It is an amenable number.

1991015321 is a deficient number, since it is larger than the sum of its proper divisors (1).

1991015321 is an equidigital number, since it uses as much as digits as its factorization.

1991015321 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2430, while the sum is 32.

The square root of 1991015321 is about 44620.7947150205. The cubic root of 1991015321 is about 1258.0315532774.

The spelling of 1991015321 in words is "one billion, nine hundred ninety-one million, fifteen thousand, three hundred twenty-one".