1991623 has 2 divisors, whose sum is σ = 1991624. Its totient is φ = 1991622.

The previous prime is 1991617. The next prime is 1991641. The reversal of 1991623 is 3261991.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1991623 is a prime.

It is a zygodrome in base 2.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1991603) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 995811 + 995812.

It is an arithmetic number, because the mean of its divisors is an integer number (995812).

2^1991623 is an apocalyptic number.

1991623 is a deficient number, since it is larger than the sum of its proper divisors (1).

1991623 is an equidigital number, since it uses as much as digits as its factorization.

1991623 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2916, while the sum is 31.

The square root of 1991623 is about 1411.2487378205. The cubic root of 1991623 is about 125.8159528451.

The spelling of 1991623 in words is "one million, nine hundred ninety-one thousand, six hundred twenty-three".