21756557171 has 2 divisors, whose sum is σ = 21756557172. Its totient is φ = 21756557170.

The previous prime is 21756557149. The next prime is 21756557191. The reversal of 21756557171 is 17175565712.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21756557171 - 2¹⁴ = 21756540787 is a prime.

It is not a weakly prime, because it can be changed into another prime (21756557191) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10878278585 + 10878278586.

It is an arithmetic number, because the mean of its divisors is an integer number (10878278586).

Almost surely, 2^21756557171 is an apocalyptic number.

21756557171 is a deficient number, since it is larger than the sum of its proper divisors (1).

21756557171 is an equidigital number, since it uses as much as digits as its factorization.

21756557171 is an evil number, because the sum of its binary digits is even.

The product of its digits is 514500, while the sum is 47.

The spelling of 21756557171 in words is "twenty-one billion, seven hundred fifty-six million, five hundred fifty-seven thousand, one hundred seventy-one".