21231205555 has 16 divisors (see below), whose sum is σ = 29551668480. Its totient is φ = 14341247712.

The previous prime is 21231205547. The next prime is 21231205559. The reversal of 21231205555 is 55550213212.

It is a cyclic number.

It is not a de Polignac number, because 21231205555 - 2³ = 21231205547 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21231205559) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 4524565 + ... + 4529254.

It is an arithmetic number, because the mean of its divisors is an integer number (1846979280).

Almost surely, 2^21231205555 is an apocalyptic number.

21231205555 is a deficient number, since it is larger than the sum of its proper divisors (8320462925).

21231205555 is an equidigital number, since it uses as much as digits as its factorization.

21231205555 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9053898.

The product of its (nonzero) digits is 15000, while the sum is 31.

Adding to 21231205555 its reverse (55550213212), we get a palindrome (76781418767).

The spelling of 21231205555 in words is "twenty-one billion, two hundred thirty-one million, two hundred five thousand, five hundred fifty-five".