21131312221 has 2 divisors, whose sum is σ = 21131312222. Its totient is φ = 21131312220.

The previous prime is 21131312207. The next prime is 21131312297. The reversal of 21131312221 is 12221313112.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 16936159321 + 4195152900 = 130139^2 + 64770^2 .

It is a cyclic number.

It is not a de Polignac number, because 21131312221 - 2¹⁹ = 21130787933 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21131312201) 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 as a sum of consecutive naturals, namely, 10565656110 + 10565656111.

It is an arithmetic number, because the mean of its divisors is an integer number (10565656111).

Almost surely, 2^21131312221 is an apocalyptic number.

It is an amenable number.

21131312221 is a deficient number, since it is larger than the sum of its proper divisors (1).

21131312221 is an equidigital number, since it uses as much as digits as its factorization.

21131312221 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 144, while the sum is 19.

Adding to 21131312221 its reverse (12221313112), we get a palindrome (33352625333).

The spelling of 21131312221 in words is "twenty-one billion, one hundred thirty-one million, three hundred twelve thousand, two hundred twenty-one".