21305205642 has 64 divisors (see below), whose sum is σ = 49996364544. Its totient is φ = 5925519360.

The previous prime is 21305205641. The next prime is 21305205721. The reversal of 21305205642 is 24650250312.

It is not an unprimeable number, because it can be changed into a prime (21305205641) 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 31 ways as a sum of consecutive naturals, for example, 773418 + ... + 800490.

It is an arithmetic number, because the mean of its divisors is an integer number (781193196).

Almost surely, 2^21305205642 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21305205642, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24998182272).

21305205642 is an abundant number, since it is smaller than the sum of its proper divisors (28691158902).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21305205642 is a wasteful number, since it uses less digits than its factorization.

21305205642 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 27583.

The product of its (nonzero) digits is 14400, while the sum is 30.

Adding to 21305205642 its reverse (24650250312), we get a palindrome (45955455954).

The spelling of 21305205642 in words is "twenty-one billion, three hundred five million, two hundred five thousand, six hundred forty-two".