21747105917 has 2 divisors, whose sum is σ = 21747105918. Its totient is φ = 21747105916.

The previous prime is 21747105911. The next prime is 21747105971. The reversal of 21747105917 is 71950174712.

Together with next prime (21747105971) it forms an Ormiston pair, because they use the same digits, order apart.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 16386816121 + 5360289796 = 128011^2 + 73214^2 .

It is a cyclic number.

It is not a de Polignac number, because 21747105917 - 2²² = 21742911613 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21747105911) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10873552958 + 10873552959.

It is an arithmetic number, because the mean of its divisors is an integer number (10873552959).

Almost surely, 2^21747105917 is an apocalyptic number.

It is an amenable number.

21747105917 is a deficient number, since it is larger than the sum of its proper divisors (1).

21747105917 is an equidigital number, since it uses as much as digits as its factorization.

21747105917 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 123480, while the sum is 44.

Adding to 21747105917 its sum of digits (44), we get a square (21747105961 = 147469²).

The spelling of 21747105917 in words is "twenty-one billion, seven hundred forty-seven million, one hundred five thousand, nine hundred seventeen".