1991817 has 8 divisors (see below), whose sum is σ = 2950880. Its totient is φ = 1327860.

The previous prime is 1991797. The next prime is 1991819. The reversal of 1991817 is 7181991.

It is not a de Polignac number, because 1991817 - 2⁶ = 1991753 is a prime.

It is a super-2 number, since 2×1991817² = 7934669922978, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1991819) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 36859 + ... + 36912.

It is an arithmetic number, because the mean of its divisors is an integer number (368860).

2^1991817 is an apocalyptic number.

It is an amenable number.

1991817 is a deficient number, since it is larger than the sum of its proper divisors (959063).

1991817 is an equidigital number, since it uses as much as digits as its factorization.

1991817 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 73780 (or 73774 counting only the distinct ones).

The product of its digits is 4536, while the sum is 36.

The square root of 1991817 is about 1411.3174696007. The cubic root of 1991817 is about 125.8200378723.

It can be divided in two parts, 199 and 1817, that added together give a triangular number (2016 = T₆₃).

The spelling of 1991817 in words is "one million, nine hundred ninety-one thousand, eight hundred seventeen".