1231891691 has 4 divisors (see below), whose sum is σ = 1232715000. Its totient is φ = 1231068384.

The previous prime is 1231891663. The next prime is 1231891697. The reversal of 1231891691 is 1961981321.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 1231891691 - 2¹⁸ = 1231629547 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1231891697) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 409406 + ... + 412403.

It is an arithmetic number, because the mean of its divisors is an integer number (308178750).

Almost surely, 2^1231891691 is an apocalyptic number.

1231891691 is a deficient number, since it is larger than the sum of its proper divisors (823309).

1231891691 is an equidigital number, since it uses as much as digits as its factorization.

1231891691 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 823308.

The product of its digits is 23328, while the sum is 41.

The square root of 1231891691 is about 35098.3146461479. The cubic root of 1231891691 is about 1071.9902663383.

The spelling of 1231891691 in words is "one billion, two hundred thirty-one million, eight hundred ninety-one thousand, six hundred ninety-one".