21665952 has 144 divisors (see below), whose sum is σ = 76894272. Its totient is φ = 5621760.

The previous prime is 21665951. The next prime is 21665989. The reversal of 21665952 is 25956612.

21665952 is a `hidden beast` number, since 2 + 1 + 66 + 595 + 2 = 666.

It is a tau number, because it is divible by the number of its divisors (144).

It is a Harshad number since it is a multiple of its sum of digits (36).

It is not an unprimeable number, because it can be changed into a prime (21665951) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 21688 + ... + 22664.

It is an arithmetic number, because the mean of its divisors is an integer number (533988).

Almost surely, 2^21665952 is an apocalyptic number.

21665952 is a gapful number since it is divisible by the number (22) 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 21665952, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (38447136).

21665952 is an abundant number, since it is smaller than the sum of its proper divisors (55228320).

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

21665952 is a wasteful number, since it uses less digits than its factorization.

21665952 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1011 (or 1000 counting only the distinct ones).

The product of its digits is 32400, while the sum is 36.

The square root of 21665952 is about 4654.6699131088. The cubic root of 21665952 is about 278.7784883778.

It can be divided in two parts, 2166 and 5952, that added together give a palindrome (8118).

The spelling of 21665952 in words is "twenty-one million, six hundred sixty-five thousand, nine hundred fifty-two".