21121122221 has 2 divisors, whose sum is σ = 21121122222. Its totient is φ = 21121122220.

The previous prime is 21121122199. The next prime is 21121122241. The reversal of 21121122221 is 12222112112.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20509104100 + 612018121 = 143210^2 + 24739^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21121122221 is a prime.

It is a super-2 number, since 2×21121122221² (a number of 21 digits) contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 21121122221.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21121122241) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10560561110 + 10560561111.

It is an arithmetic number, because the mean of its divisors is an integer number (10560561111).

Almost surely, 2^21121122221 is an apocalyptic number.

It is an amenable number.

21121122221 is a deficient number, since it is larger than the sum of its proper divisors (1).

21121122221 is an equidigital number, since it uses as much as digits as its factorization.

21121122221 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 64, while the sum is 17.

Adding to 21121122221 its reverse (12222112112), we get a palindrome (33343234333).

The spelling of 21121122221 in words is "twenty-one billion, one hundred twenty-one million, one hundred twenty-two thousand, two hundred twenty-one".