21205473681 has 48 divisors (see below), whose sum is σ = 33553548864. Its totient is φ = 11873586816.

The previous prime is 21205473673. The next prime is 21205473683. The reversal of 21205473681 is 18637450212.

It is not a de Polignac number, because 21205473681 - 2³ = 21205473673 is a prime.

It is a super-2 number, since 2×21205473681² (a number of 21 digits) contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21205473683) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 9246771 + ... + 9249063.

It is an arithmetic number, because the mean of its divisors is an integer number (699032268).

Almost surely, 2^21205473681 is an apocalyptic number.

21205473681 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21205473681 is a deficient number, since it is larger than the sum of its proper divisors (12348075183).

21205473681 is a wasteful number, since it uses less digits than its factorization.

21205473681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3550 (or 3543 counting only the distinct ones).

The product of its (nonzero) digits is 80640, while the sum is 39.

The spelling of 21205473681 in words is "twenty-one billion, two hundred five million, four hundred seventy-three thousand, six hundred eighty-one".