16721993 has 2 divisors, whose sum is σ = 16721994. Its totient is φ = 16721992.

The previous prime is 16721981. The next prime is 16722023. The reversal of 16721993 is 39912761.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 8809024 + 7912969 = 2968^2 + 2813^2 .

It is a cyclic number.

It is not a de Polignac number, because 16721993 - 2⁸ = 16721737 is a prime.

It is not a weakly prime, because it can be changed into another prime (16721923) 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, 8360996 + 8360997.

It is an arithmetic number, because the mean of its divisors is an integer number (8360997).

Almost surely, 2^16721993 is an apocalyptic number.

It is an amenable number.

16721993 is a deficient number, since it is larger than the sum of its proper divisors (1).

16721993 is an equidigital number, since it uses as much as digits as its factorization.

16721993 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 20412, while the sum is 38.

The square root of 16721993 is about 4089.2533548314. The cubic root of 16721993 is about 255.7188125572.

The spelling of 16721993 in words is "sixteen million, seven hundred twenty-one thousand, nine hundred ninety-three".