19965657581 has 2 divisors, whose sum is σ = 19965657582. Its totient is φ = 19965657580.

The previous prime is 19965657499. The next prime is 19965657623. The reversal of 19965657581 is 18575656991.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 10508095081 + 9457562500 = 102509^2 + 97250^2 .

It is an emirp because it is prime and its reverse (18575656991) is a distict prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-19965657581 is a prime.

It is a super-2 number, since 2×19965657581² (a number of 21 digits) contains 22 as substring.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (19965653581) 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, 9982828790 + 9982828791.

It is an arithmetic number, because the mean of its divisors is an integer number (9982828791).

Almost surely, 2^19965657581 is an apocalyptic number.

It is an amenable number.

19965657581 is a deficient number, since it is larger than the sum of its proper divisors (1).

19965657581 is an equidigital number, since it uses as much as digits as its factorization.

19965657581 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 20412000, while the sum is 62.

The spelling of 19965657581 in words is "nineteen billion, nine hundred sixty-five million, six hundred fifty-seven thousand, five hundred eighty-one".