81216166584881 has 2 divisors, whose sum is σ = 81216166584882. Its totient is φ = 81216166584880.

The previous prime is 81216166584863. The next prime is 81216166584893. The reversal of 81216166584881 is 18848566161218.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 47878926691600 + 33337239893281 = 6919460^2 + 5773841^2 .

It is a cyclic number.

It is not a de Polignac number, because 81216166584881 - 2¹⁴ = 81216166568497 is a prime.

It is a super-2 number, since 2×81216166584881² (a number of 29 digits) contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (81216166584181) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40608083292440 + 40608083292441.

It is an arithmetic number, because the mean of its divisors is an integer number (40608083292441).

Almost surely, 2^{81216166584881} is an apocalyptic number.

It is an amenable number.

81216166584881 is a deficient number, since it is larger than the sum of its proper divisors (1).

81216166584881 is an equidigital number, since it uses as much as digits as its factorization.

81216166584881 is an evil number, because the sum of its binary digits is even.

The product of its digits is 35389440, while the sum is 65.

The spelling of 81216166584881 in words is "eighty-one trillion, two hundred sixteen billion, one hundred sixty-six million, five hundred eighty-four thousand, eight hundred eighty-one".