111781991 has 2 divisors, whose sum is σ = 111781992. Its totient is φ = 111781990.

The previous prime is 111781861. The next prime is 111782009. The reversal of 111781991 is 199187111.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 111781991 - 2¹⁴ = 111765607 is a prime.

It is a Sophie Germain prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (111781291) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 55890995 + 55890996.

It is an arithmetic number, because the mean of its divisors is an integer number (55890996).

Almost surely, 2^111781991 is an apocalyptic number.

111781991 is a deficient number, since it is larger than the sum of its proper divisors (1).

111781991 is an equidigital number, since it uses as much as digits as its factorization.

111781991 is an evil number, because the sum of its binary digits is even.

The product of its digits is 4536, while the sum is 38.

The square root of 111781991 is about 10572.7002700351. The cubic root of 111781991 is about 481.7154921244.

The spelling of 111781991 in words is "one hundred eleven million, seven hundred eighty-one thousand, nine hundred ninety-one".