1991837 has 2 divisors, whose sum is σ = 1991838. Its totient is φ = 1991836.

The previous prime is 1991819. The next prime is 1991849. The reversal of 1991837 is 7381991.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1792921 + 198916 = 1339^2 + 446^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1991837 is a prime.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 1991837.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1991137) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 995918 + 995919.

It is an arithmetic number, because the mean of its divisors is an integer number (995919).

2^1991837 is an apocalyptic number.

It is an amenable number.

1991837 is a deficient number, since it is larger than the sum of its proper divisors (1).

1991837 is an equidigital number, since it uses as much as digits as its factorization.

1991837 is an evil number, because the sum of its binary digits is even.

The product of its digits is 13608, while the sum is 38.

The square root of 1991837 is about 1411.3245551609. The cubic root of 1991837 is about 125.8204589940.

It can be divided in two parts, 199 and 1837, that multiplied together give a palindrome (365563).

The spelling of 1991837 in words is "one million, nine hundred ninety-one thousand, eight hundred thirty-seven".