21639671947 has 4 divisors (see below), whose sum is σ = 21653447976. Its totient is φ = 21625895920.

The previous prime is 21639671857. The next prime is 21639671951. The reversal of 21639671947 is 74917693612.

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

It is a cyclic number.

It is not a de Polignac number, because 21639671947 - 2³¹ = 19492188299 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21639671987) 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, 6885658 + ... + 6888799.

It is an arithmetic number, because the mean of its divisors is an integer number (5413361994).

Almost surely, 2^21639671947 is an apocalyptic number.

21639671947 is a deficient number, since it is larger than the sum of its proper divisors (13776029).

21639671947 is a wasteful number, since it uses less digits than its factorization.

21639671947 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 13776028.

The product of its digits is 3429216, while the sum is 55.

The spelling of 21639671947 in words is "twenty-one billion, six hundred thirty-nine million, six hundred seventy-one thousand, nine hundred forty-seven".