81381217 has 2 divisors, whose sum is σ = 81381218. Its totient is φ = 81381216.

The previous prime is 81381211. The next prime is 81381257. The reversal of 81381217 is 71218318.

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., 78872161 + 2509056 = 8881^2 + 1584^2 .

It is a cyclic number.

It is not a de Polignac number, because 81381217 - 2¹⁹ = 80856929 is a prime.

It is not a weakly prime, because it can be changed into another prime (81381211) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40690608 + 40690609.

It is an arithmetic number, because the mean of its divisors is an integer number (40690609).

Almost surely, 2^81381217 is an apocalyptic number.

It is an amenable number.

81381217 is a deficient number, since it is larger than the sum of its proper divisors (1).

81381217 is an equidigital number, since it uses as much as digits as its factorization.

81381217 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2688, while the sum is 31.

The square root of 81381217 is about 9021.1538618959. The cubic root of 81381217 is about 433.3525868500.

The spelling of 81381217 in words is "eighty-one million, three hundred eighty-one thousand, two hundred seventeen".