1099991 has 4 divisors (see below), whose sum is σ = 1110984. Its totient is φ = 1089000.

The previous prime is 1099961. The next prime is 1099997. The reversal of 1099991 is 1999901.

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: 1999901 = 101 ⋅19801.

It is a cyclic number.

It is not a de Polignac number, because 1099991 - 2⁶ = 1099927 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 (1099997) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 5345 + ... + 5546.

It is an arithmetic number, because the mean of its divisors is an integer number (277746).

2^1099991 is an apocalyptic number.

1099991 is a deficient number, since it is larger than the sum of its proper divisors (10993).

1099991 is a wasteful number, since it uses less digits than its factorization.

1099991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10992.

The product of its (nonzero) digits is 6561, while the sum is 38.

The square root of 1099991 is about 1048.8045575797. The cubic root of 1099991 is about 103.2277300139.

It can be divided in two parts, 10 and 99991, that added together give a palindrome (100001).

The spelling of 1099991 in words is "one million, ninety-nine thousand, nine hundred ninety-one".