21128723 has 16 divisors (see below), whose sum is σ = 26453760. Its totient is φ = 16394400.

The previous prime is 21128719. The next prime is 21128747. The reversal of 21128723 is 32782112.

It is not a de Polignac number, because 21128723 - 2² = 21128719 is a prime.

It is a super-2 number, since 2×21128723² = 892845871221458, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21128692 and 21128701.

It is not an unprimeable number, because it can be changed into a prime (21128923) 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, 25073 + ... + 25901.

It is an arithmetic number, because the mean of its divisors is an integer number (1653360).

Almost surely, 2^21128723 is an apocalyptic number.

21128723 is a deficient number, since it is larger than the sum of its proper divisors (5325037).

21128723 is a wasteful number, since it uses less digits than its factorization.

21128723 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1178.

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

The square root of 21128723 is about 4596.5990688769. The cubic root of 21128723 is about 276.4549792793.

The spelling of 21128723 in words is "twenty-one million, one hundred twenty-eight thousand, seven hundred twenty-three".