1231865891 has 2 divisors, whose sum is σ = 1231865892. Its totient is φ = 1231865890.

The previous prime is 1231865801. The next prime is 1231865959. The reversal of 1231865891 is 1985681321.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 1231865891 - 2³⁰ = 158124067 is a prime.

It is not a weakly prime, because it can be changed into another prime (1231865801) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 615932945 + 615932946.

It is an arithmetic number, because the mean of its divisors is an integer number (615932946).

Almost surely, 2^1231865891 is an apocalyptic number.

1231865891 is a deficient number, since it is larger than the sum of its proper divisors (1).

1231865891 is an equidigital number, since it uses as much as digits as its factorization.

1231865891 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 103680, while the sum is 44.

The square root of 1231865891 is about 35097.9471052083. The cubic root of 1231865891 is about 1071.9827825792.

The spelling of 1231865891 in words is "one billion, two hundred thirty-one million, eight hundred sixty-five thousand, eight hundred ninety-one".