21646221 has 16 divisors (see below), whose sum is σ = 29826048. Its totient is φ = 13953600.

The previous prime is 21646199. The next prime is 21646231. The reversal of 21646221 is 12264612.

It is not a de Polignac number, because 21646221 - 2⁵ = 21646189 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21646191 and 21646200.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21646231) 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, 20691 + ... + 21711.

It is an arithmetic number, because the mean of its divisors is an integer number (1864128).

Almost surely, 2^21646221 is an apocalyptic number.

It is an amenable number.

21646221 is a deficient number, since it is larger than the sum of its proper divisors (8179827).

21646221 is a wasteful number, since it uses less digits than its factorization.

21646221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1252.

The product of its digits is 1152, while the sum is 24.

The square root of 21646221 is about 4652.5499459974. The cubic root of 21646221 is about 278.6938356013.

It can be divided in two parts, 2164 and 6221, that added together give a triangular number (8385 = T₁₂₉).

The spelling of 21646221 in words is "twenty-one million, six hundred forty-six thousand, two hundred twenty-one".