21651223 has 4 divisors (see below), whose sum is σ = 23619528. Its totient is φ = 19682920.

The previous prime is 21651221. The next prime is 21651271. The reversal of 21651223 is 32215612.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21651223 - 2¹ = 21651221 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21651194 and 21651203.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21651221) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 984136 + ... + 984157.

It is an arithmetic number, because the mean of its divisors is an integer number (5904882).

Almost surely, 2^21651223 is an apocalyptic number.

21651223 is a deficient number, since it is larger than the sum of its proper divisors (1968305).

21651223 is a wasteful number, since it uses less digits than its factorization.

21651223 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1968304.

The product of its digits is 720, while the sum is 22.

The square root of 21651223 is about 4653.0874696270. The cubic root of 21651223 is about 278.7153007677.

Adding to 21651223 its reverse (32215612), we get a palindrome (53866835).

It can be divided in two parts, 2 and 1651223, that added together give a square (1651225 = 1285²).

The spelling of 21651223 in words is "twenty-one million, six hundred fifty-one thousand, two hundred twenty-three".