21042355665 has 16 divisors (see below), whose sum is σ = 34384105728. Its totient is φ = 10983810816.

The previous prime is 21042355661. The next prime is 21042355679. The reversal of 21042355665 is 56655324012.

It is not a de Polignac number, because 21042355665 - 2² = 21042355661 is a prime.

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 15 ways as a sum of consecutive naturals, for example, 14922952 + ... + 14924361.

It is an arithmetic number, because the mean of its divisors is an integer number (2149006608).

Almost surely, 2^21042355665 is an apocalyptic number.

It is an amenable number.

21042355665 is a deficient number, since it is larger than the sum of its proper divisors (13341750063).

21042355665 is a wasteful number, since it uses less digits than its factorization.

21042355665 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 29847368.

The product of its (nonzero) digits is 216000, while the sum is 39.

Adding to 21042355665 its reverse (56655324012), we get a palindrome (77697679677).

The spelling of 21042355665 in words is "twenty-one billion, forty-two million, three hundred fifty-five thousand, six hundred sixty-five".