21356123105 has 4 divisors (see below), whose sum is σ = 25627347732. Its totient is φ = 17084898480.

The previous prime is 21356123099. The next prime is 21356123111. The reversal of 21356123105 is 50132165312.

It is a semiprime because it is the product of two primes.

It is an interprime number because it is at equal distance from previous prime (21356123099) and next prime (21356123111).

It can be written as a sum of positive squares in 2 ways, for example, as 15040324321 + 6315798784 = 122639^2 + 79472^2 .

It is not a de Polignac number, because 21356123105 - 2¹² = 21356119009 is a prime.

It is a Duffinian number.

It is an unprimeable number.

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 in 3 ways as a sum of consecutive naturals, for example, 2135612306 + ... + 2135612315.

It is an arithmetic number, because the mean of its divisors is an integer number (6406836933).

Almost surely, 2^21356123105 is an apocalyptic number.

It is an amenable number.

21356123105 is a deficient number, since it is larger than the sum of its proper divisors (4271224627).

21356123105 is an equidigital number, since it uses as much as digits as its factorization.

21356123105 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4271224626.

The product of its (nonzero) digits is 5400, while the sum is 29.

Adding to 21356123105 its reverse (50132165312), we get a palindrome (71488288417).

The spelling of 21356123105 in words is "twenty-one billion, three hundred fifty-six million, one hundred twenty-three thousand, one hundred five".