16721531 has 4 divisors (see below), whose sum is σ = 16729752. Its totient is φ = 16713312.

The previous prime is 16721479. The next prime is 16721569. The reversal of 16721531 is 13512761.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 13512761 = 67 ⋅201683.

It is a cyclic number.

It is not a de Polignac number, because 16721531 - 2¹⁴ = 16705147 is a prime.

It is a super-2 number, since 2×16721531² = 559219197967922, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 16721531.

It is not an unprimeable number, because it can be changed into a prime (16726531) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1436 + ... + 5958.

It is an arithmetic number, because the mean of its divisors is an integer number (4182438).

Almost surely, 2^16721531 is an apocalyptic number.

16721531 is a deficient number, since it is larger than the sum of its proper divisors (8221).

16721531 is an equidigital number, since it uses as much as digits as its factorization.

16721531 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8220.

The product of its digits is 1260, while the sum is 26.

The square root of 16721531 is about 4089.1968649113. The cubic root of 16721531 is about 255.7164575114.

The spelling of 16721531 in words is "sixteen million, seven hundred twenty-one thousand, five hundred thirty-one".