16378721 has 4 divisors (see below), whose sum is σ = 16778244. Its totient is φ = 15979200.

The previous prime is 16378717. The next prime is 16378723. The reversal of 16378721 is 12787361.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 12787361 = 19 ⋅673019.

It can be written as a sum of positive squares in 2 ways, for example, as 1254400 + 15124321 = 1120^2 + 3889^2 .

It is a cyclic number.

It is not a de Polignac number, because 16378721 - 2² = 16378717 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (16378723) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 199700 + ... + 199781.

It is an arithmetic number, because the mean of its divisors is an integer number (4194561).

Almost surely, 2^16378721 is an apocalyptic number.

It is an amenable number.

16378721 is a deficient number, since it is larger than the sum of its proper divisors (399523).

16378721 is an equidigital number, since it uses as much as digits as its factorization.

16378721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 399522.

The product of its digits is 14112, while the sum is 35.

The square root of 16378721 is about 4047.0632562390. The cubic root of 16378721 is about 253.9568870964.

The spelling of 16378721 in words is "sixteen million, three hundred seventy-eight thousand, seven hundred twenty-one".