21641816 has 64 divisors (see below), whose sum is σ = 49766400. Its totient is φ = 8612352.

The previous prime is 21641797. The next prime is 21641831. The reversal of 21641816 is 61814612.

21641816 = T₁₅₃ + T₁₅₄ + ... + T₅₁₀.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 120815 + ... + 120993.

It is an arithmetic number, because the mean of its divisors is an integer number (777600).

Almost surely, 2^21641816 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21641816, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24883200).

21641816 is an abundant number, since it is smaller than the sum of its proper divisors (28124584).

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

21641816 is a wasteful number, since it uses less digits than its factorization.

21641816 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 336 (or 332 counting only the distinct ones).

The product of its digits is 2304, while the sum is 29.

The square root of 21641816 is about 4652.0765255959. The cubic root of 21641816 is about 278.6749296126.

The spelling of 21641816 in words is "twenty-one million, six hundred forty-one thousand, eight hundred sixteen".