21123355554 has 64 divisors (see below), whose sum is σ = 54955111680. Its totient is φ = 5888039040.

The previous prime is 21123355543. The next prime is 21123355571. The reversal of 21123355554 is 45555332112.

21123355554 is a `hidden beast` number, since 21 + 1 + 2 + 33 + 55 + 554 = 666.

It is a super-2 number, since 2×21123355554² (a number of 21 digits) contains 22 as substring.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 665989 + ... + 696984.

It is an arithmetic number, because the mean of its divisors is an integer number (858673620).

Almost surely, 2^21123355554 is an apocalyptic number.

21123355554 is an abundant number, since it is smaller than the sum of its proper divisors (33831756126).

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

21123355554 is a wasteful number, since it uses less digits than its factorization.

21123355554 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1363032 (or 1363026 counting only the distinct ones).

The product of its digits is 90000, while the sum is 36.

Adding to 21123355554 its reverse (45555332112), we get a palindrome (66678687666).

The spelling of 21123355554 in words is "twenty-one billion, one hundred twenty-three million, three hundred fifty-five thousand, five hundred fifty-four".