21666750721 has 8 divisors (see below), whose sum is σ = 27013091904. Its totient is φ = 16883182320.

The previous prime is 21666750673. The next prime is 21666750731. The reversal of 21666750721 is 12705766612.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21666750721 - 2¹³ = 21666742529 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21666750731) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 140693110 + ... + 140693263.

It is an arithmetic number, because the mean of its divisors is an integer number (3376636488).

Almost surely, 2^21666750721 is an apocalyptic number.

It is an amenable number.

21666750721 is a deficient number, since it is larger than the sum of its proper divisors (5346341183).

21666750721 is a wasteful number, since it uses less digits than its factorization.

21666750721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 281386391.

The product of its (nonzero) digits is 211680, while the sum is 43.

The spelling of 21666750721 in words is "twenty-one billion, six hundred sixty-six million, seven hundred fifty thousand, seven hundred twenty-one".