21505780105 has 4 divisors (see below), whose sum is σ = 25806936132. Its totient is φ = 17204624080.

The previous prime is 21505780069. The next prime is 21505780111. The reversal of 21505780105 is 50108750512.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 13700234304 + 7805545801 = 117048^2 + 88349^2 .

It is not a de Polignac number, because 21505780105 - 2¹¹ = 21505778057 is a prime.

It is a super-2 number, since 2×21505780105² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2150578006 + ... + 2150578015.

It is an arithmetic number, because the mean of its divisors is an integer number (6451734033).

Almost surely, 2^21505780105 is an apocalyptic number.

It is an amenable number.

21505780105 is a deficient number, since it is larger than the sum of its proper divisors (4301156027).

21505780105 is an equidigital number, since it uses as much as digits as its factorization.

21505780105 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4301156026.

The product of its (nonzero) digits is 14000, while the sum is 34.

The spelling of 21505780105 in words is "twenty-one billion, five hundred five million, seven hundred eighty thousand, one hundred five".