21551616451 has 4 divisors (see below), whose sum is σ = 21579497712. Its totient is φ = 21523735192.

The previous prime is 21551616413. The next prime is 21551616473. The reversal of 21551616451 is 15461615512.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21551616451 is a prime.

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 21551616451.

It is not an unprimeable number, because it can be changed into a prime (21551616851) 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, 13939471 + ... + 13941016.

It is an arithmetic number, because the mean of its divisors is an integer number (5394874428).

Almost surely, 2^21551616451 is an apocalyptic number.

21551616451 is a deficient number, since it is larger than the sum of its proper divisors (27881261).

21551616451 is an equidigital number, since it uses as much as digits as its factorization.

21551616451 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 27881260.

The product of its digits is 36000, while the sum is 37.

It can be divided in two parts, 2155161 and 6451, that added together give a palindrome (2161612).

The spelling of 21551616451 in words is "twenty-one billion, five hundred fifty-one million, six hundred sixteen thousand, four hundred fifty-one".