16851687021 has 24 divisors (see below), whose sum is σ = 26326283256. Its totient is φ = 10325744640.

The previous prime is 16851687011. The next prime is 16851687071. The reversal of 16851687021 is 12078615861.

16851687021 is a `hidden beast` number, since 1 + 68 + 516 + 8 + 70 + 2 + 1 = 666.

It can be written as a sum of positive squares in 4 ways, for example, as 2262429225 + 14589257796 = 47565^2 + 120786^2 .

It is not a de Polignac number, because 16851687021 - 2²³ = 16843298413 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (16851687011) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 281820 + ... + 336341.

It is an arithmetic number, because the mean of its divisors is an integer number (1096928469).

Almost surely, 2^16851687021 is an apocalyptic number.

It is an amenable number.

16851687021 is a deficient number, since it is larger than the sum of its proper divisors (9474596235).

16851687021 is a wasteful number, since it uses less digits than its factorization.

16851687021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 618413 (or 618410 counting only the distinct ones).

The product of its (nonzero) digits is 161280, while the sum is 45.

The spelling of 16851687021 in words is "sixteen billion, eight hundred fifty-one million, six hundred eighty-seven thousand, twenty-one".