21679728 has 80 divisors (see below), whose sum is σ = 64686336. Its totient is φ = 6128640.

The previous prime is 21679717. The next prime is 21679739. The reversal of 21679728 is 82797612.

It is an interprime number because it is at equal distance from previous prime (21679717) and next prime (21679739).

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

It is a self number, because there is not a number n which added to its sum of digits gives 21679728.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 37683 + ... + 38253.

Almost surely, 2^21679728 is an apocalyptic number.

21679728 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 21679728, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32343168).

21679728 is an abundant number, since it is smaller than the sum of its proper divisors (43006608).

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

21679728 is a wasteful number, since it uses less digits than its factorization.

21679728 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 702 (or 696 counting only the distinct ones).

The product of its digits is 84672, while the sum is 42.

The square root of 21679728 is about 4656.1494821365. The cubic root of 21679728 is about 278.8375616921.

The spelling of 21679728 in words is "twenty-one million, six hundred seventy-nine thousand, seven hundred twenty-eight".