11991997 has 2 divisors, whose sum is σ = 11991998. Its totient is φ = 11991996.

The previous prime is 11991979. The next prime is 11992037. The reversal of 11991997 is 79919911.

It is a happy number.

11991997 is digitally balanced in base 3, because in such base it contains all the possibile digits an equal number of times.

Together with previous prime (11991979) it forms an Ormiston pair, because they use the same digits, order apart.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 8173881 + 3818116 = 2859^2 + 1954^2 .

It is a cyclic number.

It is not a de Polignac number, because 11991997 - 2²³ = 3603389 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (11991937) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5995998 + 5995999.

It is an arithmetic number, because the mean of its divisors is an integer number (5995999).

Almost surely, 2^11991997 is an apocalyptic number.

It is an amenable number.

11991997 is a deficient number, since it is larger than the sum of its proper divisors (1).

11991997 is an equidigital number, since it uses as much as digits as its factorization.

11991997 is an evil number, because the sum of its binary digits is even.

The product of its digits is 45927, while the sum is 46.

The square root of 11991997 is about 3462.9462889280. The cubic root of 11991997 is about 228.8919419250.

The spelling of 11991997 in words is "eleven million, nine hundred ninety-one thousand, nine hundred ninety-seven".