21655560121 has 6 divisors (see below), whose sum is σ = 23449512030. Its totient is φ = 19989747648.

The previous prime is 21655560107. The next prime is 21655560149. The reversal of 21655560121 is 12106555612.

It can be written as a sum of positive squares in 3 ways, for example, as 478034496 + 21177525625 = 21864^2 + 145525^2 .

It is not a de Polignac number, because 21655560121 - 2⁷ = 21655559993 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21655560161) 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 5 ways as a sum of consecutive naturals, for example, 64069536 + ... + 64069873.

It is an arithmetic number, because the mean of its divisors is an integer number (3908252005).

Almost surely, 2^21655560121 is an apocalyptic number.

It is an amenable number.

21655560121 is a deficient number, since it is larger than the sum of its proper divisors (1793951909).

21655560121 is a wasteful number, since it uses less digits than its factorization.

21655560121 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 128139435 (or 128139422 counting only the distinct ones).

The product of its (nonzero) digits is 18000, while the sum is 34.

It can be divided in two parts, 216555 and 60121, that added together give a square (276676 = 526²).

The spelling of 21655560121 in words is "twenty-one billion, six hundred fifty-five million, five hundred sixty thousand, one hundred twenty-one".