21666721610 has 16 divisors (see below), whose sum is σ = 39002098536. Its totient is φ = 8666244288.

The previous prime is 21666721591. The next prime is 21666721631. The reversal of 21666721610 is 1612766612.

It can be written as a sum of positive squares in 4 ways, for example, as 21569915689 + 96805921 = 146867^2 + 9839^2 .

It is a Curzon number.

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, 209444 + ... + 295296.

Almost surely, 2^21666721610 is an apocalyptic number.

21666721610 is a deficient number, since it is larger than the sum of its proper divisors (17335376926).

21666721610 is a wasteful number, since it uses less digits than its factorization.

21666721610 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 111097.

The product of its (nonzero) digits is 36288, while the sum is 38.

The spelling of 21666721610 in words is "twenty-one billion, six hundred sixty-six million, seven hundred twenty-one thousand, six hundred ten".