1231991321 has 4 divisors (see below), whose sum is σ = 1343990544. Its totient is φ = 1119992100.

The previous prime is 1231991279. The next prime is 1231991339.

It is a happy number.

1231991321 is nontrivially palindromic in base 10.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1231991321 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1231991351) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 55999595 + ... + 55999616.

It is an arithmetic number, because the mean of its divisors is an integer number (335997636).

Almost surely, 2^1231991321 is an apocalyptic number.

1231991321 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

1231991321 is a deficient number, since it is larger than the sum of its proper divisors (111999223).

1231991321 is a wasteful number, since it uses less digits than its factorization.

1231991321 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 111999222.

The product of its digits is 2916, while the sum is 32.

The square root of 1231991321 is about 35099.7339163704. The cubic root of 1231991321 is about 1072.0191648505.

The spelling of 1231991321 in words is "one billion, two hundred thirty-one million, nine hundred ninety-one thousand, three hundred twenty-one".