21121306463561 has 4 divisors (see below), whose sum is σ = 21122074287300. Its totient is φ = 21120538639824.

The previous prime is 21121306463549. The next prime is 21121306463599. The reversal of 21121306463561 is 16536460312112.

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

It can be written as a sum of positive squares in 2 ways, for example, as 670507134025 + 20450799329536 = 818845^2 + 4522256^2 .

It is a cyclic number.

It is not a de Polignac number, because 21121306463561 - 2⁶ = 21121306463497 is a prime.

It is a super-2 number, since 2×21121306463561² (a number of 27 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21121306453561) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 383870606 + ... + 383925623.

It is an arithmetic number, because the mean of its divisors is an integer number (5280518571825).

Almost surely, 2^{21121306463561} is an apocalyptic number.

It is an amenable number.

21121306463561 is a deficient number, since it is larger than the sum of its proper divisors (767823739).

21121306463561 is an equidigital number, since it uses as much as digits as its factorization.

21121306463561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 767823738.

The product of its (nonzero) digits is 155520, while the sum is 41.

Adding to 21121306463561 its reverse (16536460312112), we get a palindrome (37657766775673).

The spelling of 21121306463561 in words is "twenty-one trillion, one hundred twenty-one billion, three hundred six million, four hundred sixty-three thousand, five hundred sixty-one".