1591221997 has 2 divisors, whose sum is σ = 1591221998. Its totient is φ = 1591221996.

The previous prime is 1591221893. The next prime is 1591222001. The reversal of 1591221997 is 7991221951.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1579347081 + 11874916 = 39741^2 + 3446^2 .

It is a cyclic number.

It is not a de Polignac number, because 1591221997 - 2⁷ = 1591221869 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1591291997) 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, 795610998 + 795610999.

It is an arithmetic number, because the mean of its divisors is an integer number (795610999).

Almost surely, 2^1591221997 is an apocalyptic number.

It is an amenable number.

1591221997 is a deficient number, since it is larger than the sum of its proper divisors (1).

1591221997 is an equidigital number, since it uses as much as digits as its factorization.

1591221997 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 102060, while the sum is 46.

The square root of 1591221997 is about 39890.1240534546. The cubic root of 1591221997 is about 1167.4642520620.

Subtracting from 1591221997 its sum of digits (46), we obtain a palindrome (1591221951).

The spelling of 1591221997 in words is "one billion, five hundred ninety-one million, two hundred twenty-one thousand, nine hundred ninety-seven".