21205473717 has 4 divisors (see below), whose sum is σ = 28273964960. Its totient is φ = 14136982476.

The previous prime is 21205473713. The next prime is 21205473739. The reversal of 21205473717 is 71737450212.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is not a de Polignac number, because 21205473717 - 2² = 21205473713 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 (21205473713) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3534245617 + ... + 3534245622.

It is an arithmetic number, because the mean of its divisors is an integer number (7068491240).

Almost surely, 2^21205473717 is an apocalyptic number.

It is an amenable number.

21205473717 is a deficient number, since it is larger than the sum of its proper divisors (7068491243).

21205473717 is an equidigital number, since it uses as much as digits as its factorization.

21205473717 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7068491242.

The product of its (nonzero) digits is 82320, while the sum is 39.

The spelling of 21205473717 in words is "twenty-one billion, two hundred five million, four hundred seventy-three thousand, seven hundred seventeen".