21220221 has 16 divisors (see below), whose sum is σ = 30945600. Its totient is φ = 12827520.

The previous prime is 21220219. The next prime is 21220223. The reversal of 21220221 is 12202212.

It is an interprime number because it is at equal distance from previous prime (21220219) and next prime (21220223).

It is not a de Polignac number, because 21220221 - 2¹ = 21220219 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21220197 and 21220206.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21220223) 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, 19705 + ... + 20753.

It is an arithmetic number, because the mean of its divisors is an integer number (1934100).

Almost surely, 2^21220221 is an apocalyptic number.

It is an amenable number.

21220221 is a deficient number, since it is larger than the sum of its proper divisors (9725379).

21220221 is a wasteful number, since it uses less digits than its factorization.

21220221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1676.

The product of its (nonzero) digits is 32, while the sum is 12.

The square root of 21220221 is about 4606.5411102041. The cubic root of 21220221 is about 276.8534676595.

Adding to 21220221 its reverse (12202212), we get a palindrome (33422433).

Subtracting from 21220221 its reverse (12202212), we obtain a square (9018009 = 3003²).

It can be divided in two parts, 2 and 1220221, that multiplied together give a palindrome (2440442).

The spelling of 21220221 in words is "twenty-one million, two hundred twenty thousand, two hundred twenty-one".