21505555551 has 8 divisors (see below), whose sum is σ = 29144141104. Its totient is φ = 14102003520.

The previous prime is 21505555537. The next prime is 21505555559. The reversal of 21505555551 is 15555550512.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21505555551 - 2¹⁰ = 21505554527 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21505555559) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 58758166 + ... + 58758531.

It is an arithmetic number, because the mean of its divisors is an integer number (3643017638).

Almost surely, 2^21505555551 is an apocalyptic number.

21505555551 is a deficient number, since it is larger than the sum of its proper divisors (7638585553).

21505555551 is a wasteful number, since it uses less digits than its factorization.

21505555551 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 117516761.

The product of its (nonzero) digits is 156250, while the sum is 39.

The spelling of 21505555551 in words is "twenty-one billion, five hundred five million, five hundred fifty-five thousand, five hundred fifty-one".