21042355666 has 8 divisors (see below), whose sum is σ = 31575723264. Its totient is φ = 10517114580.

The previous prime is 21042355661. The next prime is 21042355679. The reversal of 21042355666 is 66655324012.

It is a happy number.

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 (21042355661) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2025150 + ... + 2035513.

It is an arithmetic number, because the mean of its divisors is an integer number (3946965408).

Almost surely, 2^21042355666 is an apocalyptic number.

21042355666 is a deficient number, since it is larger than the sum of its proper divisors (10533367598).

21042355666 is a wasteful number, since it uses less digits than its factorization.

21042355666 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4063256.

The product of its (nonzero) digits is 259200, while the sum is 40.

Adding to 21042355666 its reverse (66655324012), we get a palindrome (87697679678).

The spelling of 21042355666 in words is "twenty-one billion, forty-two million, three hundred fifty-five thousand, six hundred sixty-six".