21666721611 has 16 divisors (see below), whose sum is σ = 30613536000. Its totient is φ = 13592399328.

The previous prime is 21666721591. The next prime is 21666721631. The reversal of 21666721611 is 11612766612.

It is an interprime number because it is at equal distance from previous prime (21666721591) and next prime (21666721631).

It is not a de Polignac number, because 21666721611 - 2⁶ = 21666721547 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21666721611.

It is not an unprimeable number, because it can be changed into a prime (21666721631) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 1267071 + ... + 1284056.

It is an arithmetic number, because the mean of its divisors is an integer number (1913346000).

Almost surely, 2^21666721611 is an apocalyptic number.

21666721611 is a deficient number, since it is larger than the sum of its proper divisors (8946814389).

21666721611 is a wasteful number, since it uses less digits than its factorization.

21666721611 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2551298.

The product of its digits is 36288, while the sum is 39.

The spelling of 21666721611 in words is "twenty-one billion, six hundred sixty-six million, seven hundred twenty-one thousand, six hundred eleven".