81643217 has 2 divisors, whose sum is σ = 81643218. Its totient is φ = 81643216.

The previous prime is 81643213. The next prime is 81643229. The reversal of 81643217 is 71234618.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 78074896 + 3568321 = 8836^2 + 1889^2 .

It is a cyclic number.

It is not a de Polignac number, because 81643217 - 2² = 81643213 is a prime.

It is a super-2 number, since 2×81643217² = 13331229764218178, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (81643213) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40821608 + 40821609.

It is an arithmetic number, because the mean of its divisors is an integer number (40821609).

Almost surely, 2^81643217 is an apocalyptic number.

It is an amenable number.

81643217 is a deficient number, since it is larger than the sum of its proper divisors (1).

81643217 is an equidigital number, since it uses as much as digits as its factorization.

81643217 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 8064, while the sum is 32.

The square root of 81643217 is about 9035.6636170234. The cubic root of 81643217 is about 433.8171361115.

The spelling of 81643217 in words is "eighty-one million, six hundred forty-three thousand, two hundred seventeen".