21605657721271 has 16 divisors (see below), whose sum is σ = 23347464717024. Its totient is φ = 19875290177664.

The previous prime is 21605657721233. The next prime is 21605657721299. The reversal of 21605657721271 is 17212775650612.

It is a cyclic number.

It is not a de Polignac number, because 21605657721271 - 2²⁹ = 21605120850359 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 (21605657721371) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 14267316 + ... + 15708838.

It is an arithmetic number, because the mean of its divisors is an integer number (1459216544814).

Almost surely, 2^{21605657721271} is an apocalyptic number.

21605657721271 is a deficient number, since it is larger than the sum of its proper divisors (1741806995753).

21605657721271 is a wasteful number, since it uses less digits than its factorization.

21605657721271 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1445490.

The product of its (nonzero) digits is 2469600, while the sum is 52.

The spelling of 21605657721271 in words is "twenty-one trillion, six hundred five billion, six hundred fifty-seven million, seven hundred twenty-one thousand, two hundred seventy-one".