21661368 has 64 divisors (see below), whose sum is σ = 57936000. Its totient is φ = 6728832.

The previous prime is 21661357. The next prime is 21661397. The reversal of 21661368 is 86316612.

It is a nude number because it is divisible by every one of its digits.

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, 30198 + ... + 30906.

It is an arithmetic number, because the mean of its divisors is an integer number (905250).

Almost surely, 2^21661368 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 21661368, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28968000).

21661368 is an abundant number, since it is smaller than the sum of its proper divisors (36274632).

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

21661368 is a wasteful number, since it uses less digits than its factorization.

21661368 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 804 (or 800 counting only the distinct ones).

The product of its digits is 10368, while the sum is 33.

The square root of 21661368 is about 4654.1774783521. The cubic root of 21661368 is about 278.7588260258.

The spelling of 21661368 in words is "twenty-one million, six hundred sixty-one thousand, three hundred sixty-eight".