21205530671 has 4 divisors (see below), whose sum is σ = 22836725352. Its totient is φ = 19574335992.

The previous prime is 21205530653. The next prime is 21205530719. The reversal of 21205530671 is 17603550212.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21205530671 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 (21205530631) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 815597321 + ... + 815597346.

It is an arithmetic number, because the mean of its divisors is an integer number (5709181338).

Almost surely, 2^21205530671 is an apocalyptic number.

21205530671 is a deficient number, since it is larger than the sum of its proper divisors (1631194681).

21205530671 is a wasteful number, since it uses less digits than its factorization.

21205530671 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1631194680.

The product of its (nonzero) digits is 12600, while the sum is 32.

The spelling of 21205530671 in words is "twenty-one billion, two hundred five million, five hundred thirty thousand, six hundred seventy-one".