81986437861 has 2 divisors, whose sum is σ = 81986437862. Its totient is φ = 81986437860.

The previous prime is 81986437849. The next prime is 81986437877. The reversal of 81986437861 is 16873468918.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 81470284900 + 516152961 = 285430^2 + 22719^2 .

It is a cyclic number.

It is not a de Polignac number, because 81986437861 - 2⁹ = 81986437349 is a prime.

It is a super-2 number, since 2×81986437861² (a number of 23 digits) contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 81986437861.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81986437811) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40993218930 + 40993218931.

It is an arithmetic number, because the mean of its divisors is an integer number (40993218931).

Almost surely, 2^81986437861 is an apocalyptic number.

It is an amenable number.

81986437861 is a deficient number, since it is larger than the sum of its proper divisors (1).

81986437861 is an equidigital number, since it uses as much as digits as its factorization.

81986437861 is an evil number, because the sum of its binary digits is even.

The product of its digits is 13934592, while the sum is 61.

The spelling of 81986437861 in words is "eighty-one billion, nine hundred eighty-six million, four hundred thirty-seven thousand, eight hundred sixty-one".