21721561066 has 16 divisors (see below), whose sum is σ = 33472908000. Its totient is φ = 10564099920.

The previous prime is 21721561039. The next prime is 21721561087. The reversal of 21721561066 is 66016512712.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (37).

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 216981 + ... + 300871.

It is an arithmetic number, because the mean of its divisors is an integer number (2092056750).

Almost surely, 2^21721561066 is an apocalyptic number.

21721561066 is a deficient number, since it is larger than the sum of its proper divisors (11751346934).

21721561066 is a wasteful number, since it uses less digits than its factorization.

21721561066 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 87429.

The product of its (nonzero) digits is 30240, while the sum is 37.

The spelling of 21721561066 in words is "twenty-one billion, seven hundred twenty-one million, five hundred sixty-one thousand, sixty-six".