1991729 has 2 divisors, whose sum is σ = 1991730. Its totient is φ = 1991728.

The previous prime is 1991723. The next prime is 1991753. The reversal of 1991729 is 9271991.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1849600 + 142129 = 1360^2 + 377^2 .

It is an emirp because it is prime and its reverse (9271991) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 1991729 - 2²⁰ = 943153 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 1991692 and 1991701.

It is not a weakly prime, because it can be changed into another prime (1991723) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 995864 + 995865.

It is an arithmetic number, because the mean of its divisors is an integer number (995865).

2^1991729 is an apocalyptic number.

It is an amenable number.

1991729 is a deficient number, since it is larger than the sum of its proper divisors (1).

1991729 is an equidigital number, since it uses as much as digits as its factorization.

1991729 is an evil number, because the sum of its binary digits is even.

The product of its digits is 10206, while the sum is 38.

The square root of 1991729 is about 1411.2862927131. The cubic root of 1991729 is about 125.8181849031.

The spelling of 1991729 in words is "one million, nine hundred ninety-one thousand, seven hundred twenty-nine".