81561416617 has 2 divisors, whose sum is σ = 81561416618. Its totient is φ = 81561416616.

The previous prime is 81561416513. The next prime is 81561416621. The reversal of 81561416617 is 71661416518.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 47612985616 + 33948431001 = 218204^2 + 184251^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81561416617 is a prime.

It is not a weakly prime, because it can be changed into another prime (81561413617) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40780708308 + 40780708309.

It is an arithmetic number, because the mean of its divisors is an integer number (40780708309).

Almost surely, 2^81561416617 is an apocalyptic number.

It is an amenable number.

81561416617 is a deficient number, since it is larger than the sum of its proper divisors (1).

81561416617 is an equidigital number, since it uses as much as digits as its factorization.

81561416617 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 241920, while the sum is 46.

Subtracting from 81561416617 its reverse (71661416518), we obtain a palindrome (9900000099).

The spelling of 81561416617 in words is "eighty-one billion, five hundred sixty-one million, four hundred sixteen thousand, six hundred seventeen".