21291648 has 96 divisors (see below), whose sum is σ = 65369760. Its totient is φ = 6014976.

The previous prime is 21291643. The next prime is 21291661. The reversal of 21291648 is 84619212.

It is a tau number, because it is divible by the number of its divisors (96).

It is not an unprimeable number, because it can be changed into a prime (21291643) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 239188 + ... + 239276.

It is an arithmetic number, because the mean of its divisors is an integer number (680935).

Almost surely, 2^21291648 is an apocalyptic number.

21291648 is a gapful number since it is divisible by the number (28) 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 21291648, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32684880).

21291648 is an abundant number, since it is smaller than the sum of its proper divisors (44078112).

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

21291648 is an frugal number, since it uses more digits than its factorization.

21291648 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 202 (or 101 counting only the distinct ones).

The product of its digits is 6912, while the sum is 33.

The square root of 21291648 is about 4614.2873772664. The cubic root of 21291648 is about 277.1637482291.

The spelling of 21291648 in words is "twenty-one million, two hundred ninety-one thousand, six hundred forty-eight".