21172717 has 2 divisors, whose sum is σ = 21172718. Its totient is φ = 21172716.

The previous prime is 21172709. The next prime is 21172733. The reversal of 21172717 is 71727112.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 16924996 + 4247721 = 4114^2 + 2061^2 .

It is a cyclic number.

It is not a de Polignac number, because 21172717 - 2³ = 21172709 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21172757) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10586358 + 10586359.

It is an arithmetic number, because the mean of its divisors is an integer number (10586359).

Almost surely, 2^21172717 is an apocalyptic number.

It is an amenable number.

21172717 is a deficient number, since it is larger than the sum of its proper divisors (1).

21172717 is an equidigital number, since it uses as much as digits as its factorization.

21172717 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1372, while the sum is 28.

The square root of 21172717 is about 4601.3820749857. The cubic root of 21172717 is about 276.6467234540.

Adding to 21172717 its reverse (71727112), we get a palindrome (92899829).

The spelling of 21172717 in words is "twenty-one million, one hundred seventy-two thousand, seven hundred seventeen".