21728994 has 32 divisors (see below), whose sum is σ = 50232960. Its totient is φ = 6137472.

The previous prime is 21728981. The next prime is 21729007. The reversal of 21728994 is 49982712.

It is an interprime number because it is at equal distance from previous prime (21728981) and next prime (21729007).

It is a Harshad number since it is a multiple of its sum of digits (42).

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 832 + ... + 6644.

It is an arithmetic number, because the mean of its divisors is an integer number (1569780).

Almost surely, 2^21728994 is an apocalyptic number.

21728994 is the 2492-nd nonagonal number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21728994, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25116480).

21728994 is an abundant number, since it is smaller than the sum of its proper divisors (28503966).

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

21728994 is a wasteful number, since it uses less digits than its factorization.

21728994 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5914.

The product of its digits is 72576, while the sum is 42.

The square root of 21728994 is about 4661.4369029303. The cubic root of 21728994 is about 279.0486162888.

It can be divided in two parts, 21728 and 994, that added together give a palindrome (22722).

The spelling of 21728994 in words is "twenty-one million, seven hundred twenty-eight thousand, nine hundred ninety-four".