21723128 has 16 divisors (see below), whose sum is σ = 46549680. Its totient is φ = 9309888.

The previous prime is 21723113. The next prime is 21723167. The reversal of 21723128 is 82132712.

It is a junction number, because it is equal to n+sod(n) for n = 21723097 and 21723106.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 193901 + ... + 194012.

It is an arithmetic number, because the mean of its divisors is an integer number (2909355).

Almost surely, 2^21723128 is an apocalyptic number.

21723128 is a gapful number since it is divisible by the number (28) formed by its first and last digit.

It is an amenable number.

21723128 is an abundant number, since it is smaller than the sum of its proper divisors (24826552).

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

21723128 is a wasteful number, since it uses less digits than its factorization.

21723128 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 387926 (or 387922 counting only the distinct ones).

The product of its digits is 1344, while the sum is 26.

The square root of 21723128 is about 4660.8076553319. The cubic root of 21723128 is about 279.0235031994.

The spelling of 21723128 in words is "twenty-one million, seven hundred twenty-three thousand, one hundred twenty-eight".