21591648 has 144 divisors (see below), whose sum is σ = 67878720. Its totient is φ = 6469632.

The previous prime is 21591643. The next prime is 21591653. The reversal of 21591648 is 84619512.

21591648 is a `hidden beast` number, since 2 + 1 + 5 + 9 + 1 + 648 = 666.

It is an interprime number because it is at equal distance from previous prime (21591643) and next prime (21591653).

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 a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21591643) 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 23 ways as a sum of consecutive naturals, for example, 273273 + ... + 273351.

It is an arithmetic number, because the mean of its divisors is an integer number (471380).

Almost surely, 2^21591648 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 21591648, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (33939360).

21591648 is an abundant number, since it is smaller than the sum of its proper divisors (46287072).

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

21591648 is a wasteful number, since it uses less digits than its factorization.

21591648 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 181 (or 170 counting only the distinct ones).

The product of its digits is 17280, while the sum is 36.

The square root of 21591648 is about 4646.6813964377. The cubic root of 21591648 is about 278.4594304357.

The spelling of 21591648 in words is "twenty-one million, five hundred ninety-one thousand, six hundred forty-eight".