21881664 has 196 divisors, whose sum is σ = 75513184. Its totient is φ = 6158592.

The previous prime is 21881663. The next prime is 21881681. The reversal of 21881664 is 46618812.

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

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

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21881663) by changing a digit.

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 27 ways as a sum of consecutive naturals, for example, 326559 + ... + 326625.

Almost surely, 2^21881664 is an apocalyptic number.

21881664 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 21881664, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (37756592).

21881664 is an abundant number, since it is smaller than the sum of its proper divisors (53631520).

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

21881664 is an frugal number, since it uses more digits than its factorization.

21881664 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 104 (or 79 counting only the distinct ones).

The product of its digits is 18432, while the sum is 36.

The square root of 21881664 is about 4677.7840907849. The cubic root of 21881664 is about 279.7006324202.

The spelling of 21881664 in words is "twenty-one million, eight hundred eighty-one thousand, six hundred sixty-four".