21808072 has 48 divisors (see below), whose sum is σ = 48430620. Its totient is φ = 9144960.

The previous prime is 21808051. The next prime is 21808081. The reversal of 21808072 is 27080812.

It can be written as a sum of positive squares in 2 ways, for example, as 20738916 + 1069156 = 4554^2 + 1034^2 .

It is a Smith number, since the sum of its digits (28) coincides with the sum of the digits of its prime factors.

It is a self number, because there is not a number n which added to its sum of digits gives 21808072.

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 11 ways as a sum of consecutive naturals, for example, 11718 + ... + 13450.

Almost surely, 2^21808072 is an apocalyptic number.

21808072 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 21808072, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24215310).

21808072 is an abundant number, since it is smaller than the sum of its proper divisors (26622548).

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

21808072 is a wasteful number, since it uses less digits than its factorization.

21808072 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1774 (or 1759 counting only the distinct ones).

The product of its (nonzero) digits is 1792, while the sum is 28.

The square root of 21808072 is about 4669.9113481950. The cubic root of 21808072 is about 279.3867189421.

Multiplying 21808072 by its sum of digits (28), we get a palindrome (610626016).

Adding to 21808072 its reverse (27080812), we get a palindrome (48888884).

The spelling of 21808072 in words is "twenty-one million, eight hundred eight thousand, seventy-two".