21653221666 has 8 divisors (see below), whose sum is σ = 32481120924. Its totient is φ = 10826181360.

The previous prime is 21653221661. The next prime is 21653221697. The reversal of 21653221666 is 66612235612.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 14013587641 + 7639634025 = 118379^2 + 87405^2 .

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

It is not an unprimeable number, because it can be changed into a prime (21653221661) 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, 147505 + ... + 255076.

Almost surely, 2^21653221666 is an apocalyptic number.

21653221666 is a deficient number, since it is larger than the sum of its proper divisors (10827899258).

21653221666 is a wasteful number, since it uses less digits than its factorization.

21653221666 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 429476.

The product of its digits is 155520, while the sum is 40.

The spelling of 21653221666 in words is "twenty-one billion, six hundred fifty-three million, two hundred twenty-one thousand, six hundred sixty-six".