21511312265 has 16 divisors (see below), whose sum is σ = 26423808768. Its totient is φ = 16803922176.

The previous prime is 21511312261. The next prime is 21511312279. The reversal of 21511312265 is 56221311512.

It is a cyclic number.

It is not a de Polignac number, because 21511312265 - 2² = 21511312261 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21511312261) by changing a digit.

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 15 ways as a sum of consecutive naturals, for example, 3947 + ... + 207456.

It is an arithmetic number, because the mean of its divisors is an integer number (1651488048).

Almost surely, 2^21511312265 is an apocalyptic number.

It is an amenable number.

21511312265 is a deficient number, since it is larger than the sum of its proper divisors (4912496503).

21511312265 is a wasteful number, since it uses less digits than its factorization.

21511312265 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 211888.

The product of its digits is 3600, while the sum is 29.

Adding to 21511312265 its reverse (56221311512), we get a palindrome (77732623777).

The spelling of 21511312265 in words is "twenty-one billion, five hundred eleven million, three hundred twelve thousand, two hundred sixty-five".