21216565455551 has 16 divisors (see below), whose sum is σ = 21568855633920. Its totient is φ = 20865330177120.

The previous prime is 21216565455499. The next prime is 21216565455623. The reversal of 21216565455551 is 15555456561212.

It is a cyclic number.

It is not a de Polignac number, because 21216565455551 - 2³⁰ = 21215491713727 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21216565455493 and 21216565455502.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21216565355551) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (29) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 513188141 + ... + 513229481.

It is an arithmetic number, because the mean of its divisors is an integer number (1348053477120).

Almost surely, 2^{21216565455551} is an apocalyptic number.

21216565455551 is a deficient number, since it is larger than the sum of its proper divisors (352290178369).

21216565455551 is a wasteful number, since it uses less digits than its factorization.

21216565455551 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 53894.

The product of its digits is 9000000, while the sum is 53.

The spelling of 21216565455551 in words is "twenty-one trillion, two hundred sixteen billion, five hundred sixty-five million, four hundred fifty-five thousand, five hundred fifty-one".