21661404665205 has 16 divisors (see below), whose sum is σ = 36165127789440. Its totient is φ = 11050455713088.

The previous prime is 21661404665183. The next prime is 21661404665213. The reversal of 21661404665205 is 50256640416612.

It is a happy number.

It is not a de Polignac number, because 21661404665205 - 2⁶ = 21661404665141 is a prime.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 31393339750 + ... + 31393340439.

It is an arithmetic number, because the mean of its divisors is an integer number (2260320486840).

Almost surely, 2^{21661404665205} is an apocalyptic number.

It is an amenable number.

21661404665205 is a deficient number, since it is larger than the sum of its proper divisors (14503723124235).

21661404665205 is a wasteful number, since it uses less digits than its factorization.

21661404665205 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 62786680220.

The product of its (nonzero) digits is 2073600, while the sum is 48.

The spelling of 21661404665205 in words is "twenty-one trillion, six hundred sixty-one billion, four hundred four million, six hundred sixty-five thousand, two hundred five".