21215331617 has 8 divisors (see below), whose sum is σ = 21799837416. Its totient is φ = 20631411072.

The previous prime is 21215331601. The next prime is 21215331653. The reversal of 21215331617 is 71613351212.

It can be written as a sum of positive squares in 4 ways, for example, as 4407764881 + 16807566736 = 66391^2 + 129644^2 .

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 21215331617 - 2⁴ = 21215331601 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21215361617) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 72308 + ... + 218309.

It is an arithmetic number, because the mean of its divisors is an integer number (2724979677).

Almost surely, 2^21215331617 is an apocalyptic number.

It is an amenable number.

21215331617 is a deficient number, since it is larger than the sum of its proper divisors (584505799).

21215331617 is a wasteful number, since it uses less digits than its factorization.

21215331617 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 292627.

The product of its digits is 7560, while the sum is 32.

Adding to 21215331617 its reverse (71613351212), we get a palindrome (92828682829).

The spelling of 21215331617 in words is "twenty-one billion, two hundred fifteen million, three hundred thirty-one thousand, six hundred seventeen".