21561712771 has 2 divisors, whose sum is σ = 21561712772. Its totient is φ = 21561712770.

The previous prime is 21561712769. The next prime is 21561712789. The reversal of 21561712771 is 17721716512.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21561712771 - 2¹ = 21561712769 is a prime.

Together with 21561712769, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (21561710771) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10780856385 + 10780856386.

It is an arithmetic number, because the mean of its divisors is an integer number (10780856386).

Almost surely, 2^21561712771 is an apocalyptic number.

21561712771 is a deficient number, since it is larger than the sum of its proper divisors (1).

21561712771 is an equidigital number, since it uses as much as digits as its factorization.

21561712771 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 41160, while the sum is 40.

The spelling of 21561712771 in words is "twenty-one billion, five hundred sixty-one million, seven hundred twelve thousand, seven hundred seventy-one".