21651742881 has 8 divisors (see below), whose sum is σ = 32076656160. Its totient is φ = 14434495236.

The previous prime is 21651742873. The next prime is 21651742919. The reversal of 21651742881 is 18824715612.

21651742881 is a `hidden beast` number, since 2 + 16 + 517 + 42 + 8 + 81 = 666.

It is not a de Polignac number, because 21651742881 - 2³ = 21651742873 is a prime.

It is a super-2 number, since 2×21651742881² (a number of 21 digits) contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21651742781) 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 in 7 ways as a sum of consecutive naturals, for example, 400958175 + ... + 400958228.

It is an arithmetic number, because the mean of its divisors is an integer number (4009582020).

Almost surely, 2^21651742881 is an apocalyptic number.

It is an amenable number.

21651742881 is a deficient number, since it is larger than the sum of its proper divisors (10424913279).

21651742881 is an equidigital number, since it uses as much as digits as its factorization.

21651742881 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 801916412 (or 801916406 counting only the distinct ones).

The product of its digits is 215040, while the sum is 45.

The spelling of 21651742881 in words is "twenty-one billion, six hundred fifty-one million, seven hundred forty-two thousand, eight hundred eighty-one".