21031312121 has 2 divisors, whose sum is σ = 21031312122. Its totient is φ = 21031312120.

The previous prime is 21031312069. The next prime is 21031312129. The reversal of 21031312121 is 12121313012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19379702521 + 1651609600 = 139211^2 + 40640^2 .

It is a cyclic number.

It is not a de Polignac number, because 21031312121 - 2¹⁴ = 21031295737 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21031312121.

It is not a weakly prime, because it can be changed into another prime (21031312129) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10515656060 + 10515656061.

It is an arithmetic number, because the mean of its divisors is an integer number (10515656061).

Almost surely, 2^21031312121 is an apocalyptic number.

It is an amenable number.

21031312121 is a deficient number, since it is larger than the sum of its proper divisors (1).

21031312121 is an equidigital number, since it uses as much as digits as its factorization.

21031312121 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 72, while the sum is 17.

Adding to 21031312121 its reverse (12121313012), we get a palindrome (33152625133).

The spelling of 21031312121 in words is "twenty-one billion, thirty-one million, three hundred twelve thousand, one hundred twenty-one".