21391128 has 80 divisors (see below), whose sum is σ = 65383560. Its totient is φ = 6480000.

The previous prime is 21391091. The next prime is 21391129. The reversal of 21391128 is 82119312.

It is a super-2 number, since 2×21391128² = 915160714224768, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (27).

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 (21391129) 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 19 ways as a sum of consecutive naturals, for example, 5628 + ... + 8628.

Almost surely, 2^21391128 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 21391128, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32691780).

21391128 is an abundant number, since it is smaller than the sum of its proper divisors (43992432).

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

21391128 is a wasteful number, since it uses less digits than its factorization.

21391128 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3030 (or 3017 counting only the distinct ones).

The product of its digits is 864, while the sum is 27.

The square root of 21391128 is about 4625.0543780587. The cubic root of 21391128 is about 277.5947375583.

The spelling of 21391128 in words is "twenty-one million, three hundred ninety-one thousand, one hundred twenty-eight".