21530217173 has 2 divisors, whose sum is σ = 21530217174. Its totient is φ = 21530217172.

The previous prime is 21530217143. The next prime is 21530217221. The reversal of 21530217173 is 37171203512.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 14582494564 + 6947722609 = 120758^2 + 83353^2 .

It is a cyclic number.

It is not a de Polignac number, because 21530217173 - 2²⁰ = 21529168597 is a prime.

It is a super-2 number, since 2×21530217173² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21530217133) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10765108586 + 10765108587.

It is an arithmetic number, because the mean of its divisors is an integer number (10765108587).

Almost surely, 2^21530217173 is an apocalyptic number.

It is an amenable number.

21530217173 is a deficient number, since it is larger than the sum of its proper divisors (1).

21530217173 is an equidigital number, since it uses as much as digits as its factorization.

21530217173 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 8820, while the sum is 32.

The spelling of 21530217173 in words is "twenty-one billion, five hundred thirty million, two hundred seventeen thousand, one hundred seventy-three".