1231378891 has 2 divisors, whose sum is σ = 1231378892. Its totient is φ = 1231378890.

The previous prime is 1231378861. The next prime is 1231378921. The reversal of 1231378891 is 1988731321.

It is a balanced prime because it is at equal distance from previous prime (1231378861) and next prime (1231378921).

It is an emirp because it is prime and its reverse (1988731321) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 1231378891 - 2¹¹ = 1231376843 is a prime.

It is not a weakly prime, because it can be changed into another prime (1231378861) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 615689445 + 615689446.

It is an arithmetic number, because the mean of its divisors is an integer number (615689446).

Almost surely, 2^1231378891 is an apocalyptic number.

1231378891 is a deficient number, since it is larger than the sum of its proper divisors (1).

1231378891 is an equidigital number, since it uses as much as digits as its factorization.

1231378891 is an evil number, because the sum of its binary digits is even.

The product of its digits is 72576, while the sum is 43.

The square root of 1231378891 is about 35091.0086916863. The cubic root of 1231378891 is about 1071.8414997687.

It can be divided in two parts, 12313 and 78891, that added together give a square (91204 = 302²).

The spelling of 1231378891 in words is "one billion, two hundred thirty-one million, three hundred seventy-eight thousand, eight hundred ninety-one".