1999991 is nontrivially palindromic in base 10.
It is a sphenic number, since it is the product of 3 distinct primes.
It is a cyclic number.
It is a de Polignac number, because none of the positive numbers 2k-1999991 is a prime.
It is a Duffinian number.
It is a congruent number.
21999991 is an apocalyptic number.
1999991 is an equidigital number, since it uses as much as digits as its factorization.
1999991 is an evil number, because the sum of its binary digits is even.
The sum of its prime factors is 6133.
The square root of 1999991 is about 1414.2103803890. The cubic root of 1999991 is about 125.9919160010.
The spelling of 1999991 in words is "one million, nine hundred ninety-nine thousand, nine hundred ninety-one".