21561408 has 168 divisors, whose sum is σ = 69896736. Its totient is φ = 6297600.

The previous prime is 21561401. The next prime is 21561427. The reversal of 21561408 is 80416512.

It is not an unprimeable number, because it can be changed into a prime (21561401) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (5) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 259735 + ... + 259817.

It is an arithmetic number, because the mean of its divisors is an integer number (416052).

Almost surely, 2^21561408 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 21561408, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (34948368).

21561408 is an abundant number, since it is smaller than the sum of its proper divisors (48335328).

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

21561408 is a wasteful number, since it uses less digits than its factorization.

21561408 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 153 (or 140 counting only the distinct ones).

The product of its (nonzero) digits is 1920, while the sum is 27.

The square root of 21561408 is about 4643.4263211555. The cubic root of 21561408 is about 278.3293716991.

The spelling of 21561408 in words is "twenty-one million, five hundred sixty-one thousand, four hundred eight".