21320021617 has 4 divisors (see below), whose sum is σ = 21339966580. Its totient is φ = 21300076656.

The previous prime is 21320021539. The next prime is 21320021621. The reversal of 21320021617 is 71612002312.

It is a happy number.

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 10453835536 + 10866186081 = 102244^2 + 104241^2 .

It is a cyclic number.

It is not a de Polignac number, because 21320021617 - 2²⁷ = 21185803889 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21320021591 and 21320021600.

It is not an unprimeable number, because it can be changed into a prime (21320021117) 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, 9970878 + ... + 9973015.

It is an arithmetic number, because the mean of its divisors is an integer number (5334991645).

Almost surely, 2^21320021617 is an apocalyptic number.

It is an amenable number.

21320021617 is a deficient number, since it is larger than the sum of its proper divisors (19944963).

21320021617 is a wasteful number, since it uses less digits than its factorization.

21320021617 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 19944962.

The product of its (nonzero) digits is 1008, while the sum is 25.

Adding to 21320021617 its reverse (71612002312), we get a palindrome (92932023929).

The spelling of 21320021617 in words is "twenty-one billion, three hundred twenty million, twenty-one thousand, six hundred seventeen".