16721391 has 16 divisors (see below), whose sum is σ = 23618304. Its totient is φ = 10500864.

The previous prime is 16721357. The next prime is 16721407. The reversal of 16721391 is 19312761.

It is a de Polignac number, because none of the positive numbers 2^k-16721391 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (16721291) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 2815 + ... + 6431.

It is an arithmetic number, because the mean of its divisors is an integer number (1476144).

Almost surely, 2^16721391 is an apocalyptic number.

16721391 is a deficient number, since it is larger than the sum of its proper divisors (6896913).

16721391 is a wasteful number, since it uses less digits than its factorization.

16721391 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3710.

The product of its digits is 2268, while the sum is 30.

The square root of 16721391 is about 4089.1797465996. The cubic root of 16721391 is about 255.7157438526.

The spelling of 16721391 in words is "sixteen million, seven hundred twenty-one thousand, three hundred ninety-one".