21123661104451 has 4 divisors (see below), whose sum is σ = 21123895218192. Its totient is φ = 21123426990712.

The previous prime is 21123661104419. The next prime is 21123661104461. The reversal of 21123661104451 is 15440116632112.

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

It is a cyclic number.

It is not a de Polignac number, because 21123661104451 - 2⁵ = 21123661104419 is a prime.

It is a super-2 number, since 2×21123661104451² (a number of 27 digits) contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21123661104451.

It is not an unprimeable number, because it can be changed into a prime (21123661104401) by changing a digit.

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, 116921476 + ... + 117102001.

It is an arithmetic number, because the mean of its divisors is an integer number (5280973804548).

Almost surely, 2^{21123661104451} is an apocalyptic number.

21123661104451 is a deficient number, since it is larger than the sum of its proper divisors (234113741).

21123661104451 is an equidigital number, since it uses as much as digits as its factorization.

21123661104451 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 234113740.

The product of its (nonzero) digits is 34560, while the sum is 37.

Adding to 21123661104451 its reverse (15440116632112), we get a palindrome (36563777736563).

The spelling of 21123661104451 in words is "twenty-one trillion, one hundred twenty-three billion, six hundred sixty-one million, one hundred four thousand, four hundred fifty-one".