21221221221 has 24 divisors (see below), whose sum is σ = 31852154880. Its totient is φ = 13598345376.

The previous prime is 21221221199. The next prime is 21221221223. The reversal of 21221221221 is 12212212212.

It is a happy number.

21221221221 is a `hidden beast` number, since 2 + 1 + 221 + 221 + 221 = 666.

It is not a de Polignac number, because 21221221221 - 2⁷ = 21221221093 is a prime.

It is a super-2 number, since 2×21221221221² (a number of 21 digits) contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21221221194 and 21221221203.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21221221223) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 124101 + ... + 240506.

It is an arithmetic number, because the mean of its divisors is an integer number (1327173120).

Almost surely, 2^21221221221 is an apocalyptic number.

It is an amenable number.

21221221221 is a deficient number, since it is larger than the sum of its proper divisors (10630933659).

21221221221 is a wasteful number, since it uses less digits than its factorization.

21221221221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 364865 (or 364862 counting only the distinct ones).

The product of its digits is 128, while the sum is 18.

Adding to 21221221221 its reverse (12212212212), we get a palindrome (33433433433).

Subtracting from 21221221221 its reverse (12212212212), we obtain a palindrome (9009009009).

It can be divided in two parts, 2 and 1221221221, that multiplied together give a palindrome (2442442442).

The spelling of 21221221221 in words is "twenty-one billion, two hundred twenty-one million, two hundred twenty-one thousand, two hundred twenty-one".