21511843217 has 4 divisors (see below), whose sum is σ = 21523233060. Its totient is φ = 21500453376.

The previous prime is 21511843211. The next prime is 21511843261. The reversal of 21511843217 is 71234811512.

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 14757633361 + 6754209856 = 121481^2 + 82184^2 .

It is a cyclic number.

It is not a de Polignac number, because 21511843217 - 2⁴ = 21511843201 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21511843211) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 5692088 + ... + 5695865.

It is an arithmetic number, because the mean of its divisors is an integer number (5380808265).

Almost surely, 2^21511843217 is an apocalyptic number.

It is an amenable number.

21511843217 is a deficient number, since it is larger than the sum of its proper divisors (11389843).

21511843217 is a wasteful number, since it uses less digits than its factorization.

21511843217 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11389842.

The product of its digits is 13440, while the sum is 35.

The spelling of 21511843217 in words is "twenty-one billion, five hundred eleven million, eight hundred forty-three thousand, two hundred seventeen".