21123121013 has 2 divisors, whose sum is σ = 21123121014. Its totient is φ = 21123121012.

The previous prime is 21123121003. The next prime is 21123121043. The reversal of 21123121013 is 31012132112.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 14849372164 + 6273748849 = 121858^2 + 79207^2 .

It is a cyclic number.

It is not a de Polignac number, because 21123121013 - 2¹⁰ = 21123119989 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21123120982 and 21123121000.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21123121003) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10561560506 + 10561560507.

It is an arithmetic number, because the mean of its divisors is an integer number (10561560507).

Almost surely, 2^21123121013 is an apocalyptic number.

It is an amenable number.

21123121013 is a deficient number, since it is larger than the sum of its proper divisors (1).

21123121013 is an equidigital number, since it uses as much as digits as its factorization.

21123121013 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 21123121013 its reverse (31012132112), we get a palindrome (52135253125).

The spelling of 21123121013 in words is "twenty-one billion, one hundred twenty-three million, one hundred twenty-one thousand, thirteen".