21155332221 has 10 divisors (see below), whose sum is σ = 31602409982. Its totient is φ = 14103554760.

The previous prime is 21155332217. The next prime is 21155332267. The reversal of 21155332221 is 12223355112.

It can be written as a sum of positive squares in only one way, i.e., 16903640196 + 4251692025 = 130014^2 + 65205^2 .

It is not a de Polignac number, because 21155332221 - 2² = 21155332217 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21155312221) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 9 ways as a sum of consecutive naturals, for example, 130588390 + ... + 130588551.

Almost surely, 2^21155332221 is an apocalyptic number.

It is an amenable number.

21155332221 is a deficient number, since it is larger than the sum of its proper divisors (10447077761).

21155332221 is an equidigital number, since it uses as much as digits as its factorization.

21155332221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 261176953 (or 261176944 counting only the distinct ones).

The product of its digits is 3600, while the sum is 27.

Adding to 21155332221 its reverse (12223355112), we get a palindrome (33378687333).

The spelling of 21155332221 in words is "twenty-one billion, one hundred fifty-five million, three hundred thirty-two thousand, two hundred twenty-one".