21361728 has 112 divisors (see below), whose sum is σ = 60537344. Its totient is φ = 6635520.

The previous prime is 21361727. The next prime is 21361729. The reversal of 21361728 is 82716312.

It is an interprime number because it is at equal distance from previous prime (21361727) and next prime (21361729).

It is a junction number, because it is equal to n+sod(n) for n = 21361695 and 21361704.

It is not an unprimeable number, because it can be changed into a prime (21361721) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 220176 + ... + 220272.

It is an arithmetic number, because the mean of its divisors is an integer number (540512).

Almost surely, 2^21361728 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 21361728, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30268672).

21361728 is an abundant number, since it is smaller than the sum of its proper divisors (39175616).

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

21361728 is a wasteful number, since it uses less digits than its factorization.

21361728 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 180 (or 170 counting only the distinct ones).

The product of its digits is 4032, while the sum is 30.

The square root of 21361728 is about 4621.8749442191. The cubic root of 21361728 is about 277.4675037022.

The spelling of 21361728 in words is "twenty-one million, three hundred sixty-one thousand, seven hundred twenty-eight".