21665424 has 80 divisors (see below), whose sum is σ = 62763840. Its totient is φ = 6382080.

The previous prime is 21665401. The next prime is 21665473. The reversal of 21665424 is 42456612.

It is a super-3 number, since 3×21665424³ (a number of 23 digits) contains 333 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21665391 and 21665400.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 18982 + ... + 20090.

It is an arithmetic number, because the mean of its divisors is an integer number (784548).

Almost surely, 2^21665424 is an apocalyptic number.

21665424 is a gapful number since it is divisible by the number (24) 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 21665424, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31381920).

21665424 is an abundant number, since it is smaller than the sum of its proper divisors (41098416).

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

21665424 is a wasteful number, since it uses less digits than its factorization.

21665424 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1168 (or 1162 counting only the distinct ones).

The product of its digits is 11520, while the sum is 30.

The square root of 21665424 is about 4654.6131955298. The cubic root of 21665424 is about 278.7762237456.

The spelling of 21665424 in words is "twenty-one million, six hundred sixty-five thousand, four hundred twenty-four".