With n = 15705261201683973613 Expected 15705261201683973612 but got 83
83 is the correct answer. The random tests seem to break when the base is near 80. (I got another error where I got 84 for the base on a large number, but I did not write it down).

#[test]
fn fail12() {
dotest( 15705261201683973613, 15705261201683973612 )
}