11801991 has 4 divisors (see below), whose sum is σ = 15735992. Its totient is φ = 7867992.

The previous prime is 11801989. The next prime is 11802017. The reversal of 11801991 is 19910811.

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: 19910811 = 3 ⋅6636937.

It is not a de Polignac number, because 11801991 - 2¹ = 11801989 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (11801941) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1966996 + ... + 1967001.

It is an arithmetic number, because the mean of its divisors is an integer number (3933998).

Almost surely, 2^11801991 is an apocalyptic number.

11801991 is a deficient number, since it is larger than the sum of its proper divisors (3934001).

11801991 is an equidigital number, since it uses as much as digits as its factorization.

11801991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3934000.

The product of its (nonzero) digits is 648, while the sum is 30.

The square root of 11801991 is about 3435.4025964943. The cubic root of 11801991 is about 227.6766152578.

The spelling of 11801991 in words is "eleven million, eight hundred one thousand, nine hundred ninety-one".