21165660555 has 48 divisors (see below), whose sum is σ = 36861300576. Its totient is φ = 10365788160.

The previous prime is 21165660517. The next prime is 21165660559. The reversal of 21165660555 is 55506656112.

It is not a de Polignac number, because 21165660555 - 2¹⁰ = 21165659531 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21165660559) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 467625 + ... + 510885.

It is an arithmetic number, because the mean of its divisors is an integer number (767943762).

Almost surely, 2^21165660555 is an apocalyptic number.

21165660555 is a deficient number, since it is larger than the sum of its proper divisors (15695640021).

21165660555 is a wasteful number, since it uses less digits than its factorization.

21165660555 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 43488 (or 43475 counting only the distinct ones).

The product of its (nonzero) digits is 270000, while the sum is 42.

The spelling of 21165660555 in words is "twenty-one billion, one hundred sixty-five million, six hundred sixty thousand, five hundred fifty-five".