21688144 has 20 divisors (see below), whose sum is σ = 42258580. Its totient is φ = 10782720.

The previous prime is 21688111. The next prime is 21688159. The reversal of 21688144 is 44188612.

21688144 = 427² + 428² + ... + 522².

It can be written as a sum of positive squares in 2 ways, for example, as 4048144 + 17640000 = 2012^2 + 4200^2 .

It is a super-3 number, since 3×21688144³ (a number of 23 digits) contains 333 as substring.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 849 + ... + 6640.

It is an arithmetic number, because the mean of its divisors is an integer number (2112929).

Almost surely, 2^21688144 is an apocalyptic number.

It is an amenable number.

21688144 is a deficient number, since it is larger than the sum of its proper divisors (20570436).

21688144 is a wasteful number, since it uses less digits than its factorization.

21688144 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7678 (or 7672 counting only the distinct ones).

The product of its digits is 12288, while the sum is 34.

The square root of 21688144 is about 4657.0531454988. The cubic root of 21688144 is about 278.8736383029.

The spelling of 21688144 in words is "twenty-one million, six hundred eighty-eight thousand, one hundred forty-four".