21505205161 has 8 divisors (see below), whose sum is σ = 23506870464. Its totient is φ = 19511314320.

The previous prime is 21505205149. The next prime is 21505205203. The reversal of 21505205161 is 16150250512.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21505205161 - 2¹⁵ = 21505172393 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21505205261) by changing a digit.

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 7 ways as a sum of consecutive naturals, for example, 1937826 + ... + 1948891.

It is an arithmetic number, because the mean of its divisors is an integer number (2938358808).

Almost surely, 2^21505205161 is an apocalyptic number.

It is an amenable number.

21505205161 is a deficient number, since it is larger than the sum of its proper divisors (2001665303).

21505205161 is a wasteful number, since it uses less digits than its factorization.

21505205161 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3887231.

The product of its (nonzero) digits is 3000, while the sum is 28.

Adding to 21505205161 its reverse (16150250512), we get a palindrome (37655455673).

The spelling of 21505205161 in words is "twenty-one billion, five hundred five million, two hundred five thousand, one hundred sixty-one".