21539909717 has 2 divisors, whose sum is σ = 21539909718. Its totient is φ = 21539909716.

The previous prime is 21539909627. The next prime is 21539909737. The reversal of 21539909717 is 71790993512.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21538204081 + 1705636 = 146759^2 + 1306^2 .

It is a cyclic number.

It is not a de Polignac number, because 21539909717 - 2¹⁶ = 21539844181 is a prime.

It is a super-2 number, since 2×21539909717² (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 (21539909737) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10769954858 + 10769954859.

It is an arithmetic number, because the mean of its divisors is an integer number (10769954859).

Almost surely, 2^21539909717 is an apocalyptic number.

It is an amenable number.

21539909717 is a deficient number, since it is larger than the sum of its proper divisors (1).

21539909717 is an equidigital number, since it uses as much as digits as its factorization.

21539909717 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1071630, while the sum is 53.

The spelling of 21539909717 in words is "twenty-one billion, five hundred thirty-nine million, nine hundred nine thousand, seven hundred seventeen".