1691955721 has 4 divisors (see below), whose sum is σ = 1737684292. Its totient is φ = 1646227152.

The previous prime is 1691955689. The next prime is 1691955761. The reversal of 1691955721 is 1275591961.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 1238265721 + 453690000 = 35189^2 + 21300^2 .

It is a cyclic number.

It is not a de Polignac number, because 1691955721 - 2⁵ = 1691955689 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1691955761) 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 in 3 ways as a sum of consecutive naturals, for example, 22864230 + ... + 22864303.

It is an arithmetic number, because the mean of its divisors is an integer number (434421073).

Almost surely, 2^1691955721 is an apocalyptic number.

It is an amenable number.

1691955721 is a deficient number, since it is larger than the sum of its proper divisors (45728571).

1691955721 is an equidigital number, since it uses as much as digits as its factorization.

1691955721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 45728570.

The product of its digits is 170100, while the sum is 46.

The square root of 1691955721 is about 41133.3893692217. The cubic root of 1691955721 is about 1191.5977223179.

The spelling of 1691955721 in words is "one billion, six hundred ninety-one million, nine hundred fifty-five thousand, seven hundred twenty-one".