21655205717 has 2 divisors, whose sum is σ = 21655205718. Its totient is φ = 21655205716.

The previous prime is 21655205647. The next prime is 21655205843. The reversal of 21655205717 is 71750255612.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 19949020081 + 1706185636 = 141241^2 + 41306^2 .

It is a cyclic number.

It is not a de Polignac number, because 21655205717 - 2⁸ = 21655205461 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21655205917) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10827602858 + 10827602859.

It is an arithmetic number, because the mean of its divisors is an integer number (10827602859).

Almost surely, 2^21655205717 is an apocalyptic number.

It is an amenable number.

21655205717 is a deficient number, since it is larger than the sum of its proper divisors (1).

21655205717 is an equidigital number, since it uses as much as digits as its factorization.

21655205717 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 147000, while the sum is 41.

The spelling of 21655205717 in words is "twenty-one billion, six hundred fifty-five million, two hundred five thousand, seven hundred seventeen".