21531645173 has 2 divisors, whose sum is σ = 21531645174. Its totient is φ = 21531645172.

The previous prime is 21531645089. The next prime is 21531645199. The reversal of 21531645173 is 37154613512.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17270427889 + 4261217284 = 131417^2 + 65278^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21531645173 is a prime.

It is a super-2 number, since 2×21531645173² (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 (21531645973) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10765822586 + 10765822587.

It is an arithmetic number, because the mean of its divisors is an integer number (10765822587).

Almost surely, 2^21531645173 is an apocalyptic number.

It is an amenable number.

21531645173 is a deficient number, since it is larger than the sum of its proper divisors (1).

21531645173 is an equidigital number, since it uses as much as digits as its factorization.

21531645173 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 75600, while the sum is 38.

The spelling of 21531645173 in words is "twenty-one billion, five hundred thirty-one million, six hundred forty-five thousand, one hundred seventy-three".