21505221204 has 24 divisors (see below), whose sum is σ = 53130547008. Its totient is φ = 6746736000.

The previous prime is 21505221137. The next prime is 21505221209. The reversal of 21505221204 is 40212250512.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21505221209) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 52708672 + ... + 52709079.

It is an arithmetic number, because the mean of its divisors is an integer number (2213772792).

Almost surely, 2^21505221204 is an apocalyptic number.

It is an amenable number.

21505221204 is an abundant number, since it is smaller than the sum of its proper divisors (31625325804).

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

21505221204 is a wasteful number, since it uses less digits than its factorization.

21505221204 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 105417775 (or 105417773 counting only the distinct ones).

The product of its (nonzero) digits is 1600, while the sum is 24.

Adding to 21505221204 its reverse (40212250512), we get a palindrome (61717471716).

The spelling of 21505221204 in words is "twenty-one billion, five hundred five million, two hundred twenty-one thousand, two hundred four".