16721645 has 8 divisors (see below), whose sum is σ = 20555640. Its totient is φ = 13050880.

The previous prime is 16721641. The next prime is 16721647. The reversal of 16721645 is 54612761.

It can be written as a sum of positive squares in 4 ways, for example, as 1331716 + 15389929 = 1154^2 + 3923^2 .

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

It is not a de Polignac number, because 16721645 - 2² = 16721641 is a prime.

It is a super-3 number, since 3×16721645³ (a number of 23 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (16721641) 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 7 ways as a sum of consecutive naturals, for example, 40580 + ... + 40989.

It is an arithmetic number, because the mean of its divisors is an integer number (2569455).

Almost surely, 2^16721645 is an apocalyptic number.

It is an amenable number.

16721645 is a deficient number, since it is larger than the sum of its proper divisors (3833995).

16721645 is an equidigital number, since it uses as much as digits as its factorization.

16721645 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 81615.

The product of its digits is 10080, while the sum is 32.

The square root of 16721645 is about 4089.2108040550. The cubic root of 16721645 is about 255.7170386307.

It can be divided in two parts, 167 and 21645, that added together give a palindrome (21812).

The spelling of 16721645 in words is "sixteen million, seven hundred twenty-one thousand, six hundred forty-five".