16978921 has 8 divisors (see below), whose sum is σ = 17361864. Its totient is φ = 16598400.

The previous prime is 16978901. The next prime is 16978931. The reversal of 16978921 is 12987961.

It can be written as a sum of positive squares in 4 ways, for example, as 10653696 + 6325225 = 3264^2 + 2515^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-16978921 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (16978901) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 23871 + ... + 24571.

It is an arithmetic number, because the mean of its divisors is an integer number (2170233).

Almost surely, 2^16978921 is an apocalyptic number.

It is an amenable number.

16978921 is a deficient number, since it is larger than the sum of its proper divisors (382943).

16978921 is an equidigital number, since it uses as much as digits as its factorization.

16978921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1211.

The product of its digits is 54432, while the sum is 43.

The square root of 16978921 is about 4120.5486285202. The cubic root of 16978921 is about 257.0218405134.

The spelling of 16978921 in words is "sixteen million, nine hundred seventy-eight thousand, nine hundred twenty-one".