1688997721 has 2 divisors, whose sum is σ = 1688997722. Its totient is φ = 1688997720.

The previous prime is 1688997701. The next prime is 1688997733. The reversal of 1688997721 is 1277998861.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1330425625 + 358572096 = 36475^2 + 18936^2 .

It is a cyclic number.

It is not a de Polignac number, because 1688997721 - 2¹⁹ = 1688473433 is a prime.

It is not a weakly prime, because it can be changed into another prime (1688997701) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 844498860 + 844498861.

It is an arithmetic number, because the mean of its divisors is an integer number (844498861).

Almost surely, 2^1688997721 is an apocalyptic number.

It is an amenable number.

1688997721 is a deficient number, since it is larger than the sum of its proper divisors (1).

1688997721 is an equidigital number, since it uses as much as digits as its factorization.

1688997721 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 3048192, while the sum is 58.

The square root of 1688997721 is about 41097.4174492753. The cubic root of 1688997721 is about 1190.9029046603.

The spelling of 1688997721 in words is "one billion, six hundred eighty-eight million, nine hundred ninety-seven thousand, seven hundred twenty-one".