1231181921 has 4 divisors (see below), whose sum is σ = 1273636500. Its totient is φ = 1188727344.

The previous prime is 1231181867. The next prime is 1231181929. The reversal of 1231181921 is 1291811321.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1291811321 = 107 ⋅12073003.

It can be written as a sum of positive squares in 2 ways, for example, as 426835600 + 804346321 = 20660^2 + 28361^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1231181921 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (29), and also a Moran number because the ratio is a prime number: 42454549 = 1231181921 / (1 + 2 + 3 + 1 + 1 + 8 + 1 + 9 + 2 + 1).

It is not an unprimeable number, because it can be changed into a prime (1231181929) 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, 21227246 + ... + 21227303.

It is an arithmetic number, because the mean of its divisors is an integer number (318409125).

Almost surely, 2^1231181921 is an apocalyptic number.

It is an amenable number.

1231181921 is a deficient number, since it is larger than the sum of its proper divisors (42454579).

1231181921 is an equidigital number, since it uses as much as digits as its factorization.

1231181921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 42454578.

The product of its digits is 864, while the sum is 29.

The square root of 1231181921 is about 35088.2020200523. The cubic root of 1231181921 is about 1071.7843465292.

The spelling of 1231181921 in words is "one billion, two hundred thirty-one million, one hundred eighty-one thousand, nine hundred twenty-one".