16491721 has 9 divisors (see below), whose sum is σ = 17171949. Its totient is φ = 15837900.

The previous prime is 16491719. The next prime is 16491731. The reversal of 16491721 is 12719461.

The square root of 16491721 is 4061.

It is a perfect power (a square), and thus also a powerful number.

It is not a de Polignac number, because 16491721 - 2¹ = 16491719 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (31).

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (16491731) by changing a digit.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 125826 + ... + 125956.

Almost surely, 2^16491721 is an apocalyptic number.

16491721 is the 4061-st square number.

16491721 is the 2031-st centered octagonal number.

It is an amenable number.

16491721 is a deficient number, since it is larger than the sum of its proper divisors (680228).

16491721 is an frugal number, since it uses more digits than its factorization.

16491721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 324 (or 162 counting only the distinct ones).

The product of its digits is 3024, while the sum is 31.

The cubic root of 16491721 is about 254.5395818489.

The spelling of 16491721 in words is "sixteen million, four hundred ninety-one thousand, seven hundred twenty-one".