16721640 has 160 divisors (see below), whose sum is σ = 60679080. Its totient is φ = 4105728.

The previous prime is 16721633. The next prime is 16721641. The reversal of 16721640 is 4612761.

16721640 is a `hidden beast` number, since 16 + 7 + 2 + 1 + 640 = 666.

It can be written as a sum of positive squares in 4 ways, for example, as 11819844 + 4901796 = 3438^2 + 2214^2 .

It is a super-2 number, since 2×16721640² = 559226488579200, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (27).

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 polite number, since it can be written in 39 ways as a sum of consecutive naturals, for example, 41922 + ... + 42318.

Almost surely, 2^16721640 is an apocalyptic number.

16721640 is a gapful number since it is divisible by the number (10) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 16721640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30339540).

16721640 is an abundant number, since it is smaller than the sum of its proper divisors (43957440).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

16721640 is a wasteful number, since it uses less digits than its factorization.

16721640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 433 (or 420 counting only the distinct ones).

The product of its (nonzero) digits is 2016, while the sum is 27.

The square root of 16721640 is about 4089.2101926900. The cubic root of 16721640 is about 255.7170131430.

The spelling of 16721640 in words is "sixteen million, seven hundred twenty-one thousand, six hundred forty".