21405126121 has 2 divisors, whose sum is σ = 21405126122. Its totient is φ = 21405126120.

The previous prime is 21405126013. The next prime is 21405126143. The reversal of 21405126121 is 12162150412.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 11037813721 + 10367312400 = 105061^2 + 101820^2 .

It is a cyclic number.

It is not a de Polignac number, because 21405126121 - 2²³ = 21396737513 is a prime.

It is not a weakly prime, because it can be changed into another prime (21405126161) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10702563060 + 10702563061.

It is an arithmetic number, because the mean of its divisors is an integer number (10702563061).

Almost surely, 2^21405126121 is an apocalyptic number.

It is an amenable number.

21405126121 is a deficient number, since it is larger than the sum of its proper divisors (1).

21405126121 is an equidigital number, since it uses as much as digits as its factorization.

21405126121 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 960, while the sum is 25.

Adding to 21405126121 its reverse (12162150412), we get a palindrome (33567276533).

The spelling of 21405126121 in words is "twenty-one billion, four hundred five million, one hundred twenty-six thousand, one hundred twenty-one".