February 2015 - mathfun@mailman.xmission.com

[math-fun] Variant of Ulam's spiral
by James Propp 01 Mar '15

01 Mar '15

I recently saw an article that mentioned a variant of Ulam's spiral in which the primes magically form parabolas rather than lines. Can anyone provide a source? Thanks, Jim Propp

2 2

[math-fun] http://wstein.org/rh/
by Bill Gosper 27 Feb '15

27 Feb '15

Hi William, you could simplify the p16 proof of the infinitude of the primes. Put any positive integer (e.g.1) in a bag. Repeat forever: Include in the bag the number formed by adding 1 to the product of all the numbers already in the bag. Each new inclusion is relatively prime to all the rest, so no prime appears more than once among the factorizations. This requires an infinitude of primes. If we start with 1, it's sort of neat that the successive inclusions are 2, 3, 7, 43, ..., A000058, Sylvester's sequence, whose reciprocals sum to 1 by being the denominators of the greedy Egyptian expansion of 1-1/∞. --Bill Gosper

4 6

Re: [math-fun] Completely off-topic: home color printers ?
by Bill Gosper 27 Feb '15

27 Feb '15

TK>Unless you need photographic quality, i’d strong[ly] suggest ditching ink squirting printers. I bought a Brother MFC-9970CDW laser printer and have been extremely happy. Thanks, Tom, I'll do that! I have sworn I'll never buy another ink cartridge. I actually believe that when you turn it on, the printer software wakes up, sees how long it's been, and pees accordingly into a little sponge or something. And if one color is clogged, the "cleaning" cycle exhausts all four of them. And then there's all that anti-refill technology. And some of them won't print B&W if you're out of yellow. You should be suspicious when they practically give you the printer to begin with. --rwg On Feb 25, 2015, at 1:45 PM, Henry Baker <hbaker1(a)pipeline.com> wrote: I can't find an inexpensive _reliable_ color printer. Part of the problem is that I only need color printing every 3 months or so, at which point the previous (expensive) cartridges have always dried out. As bad as this is, at least replacing the cartridges used to work. The newer ink-jet printers now clog the ink jets themselves, and the entire printer becomes useless. There doesn't appear to be any procedure for removing & cleaning these inkjets. I spent a couple of hours looking for color inkjet printers, and it appears that all of these printers require _gigantic_ amounts of software, none of which I need, and they all want to talk directly over the internet to their manufacturers, which I also refuse to allow. Does anyone here have any suggestions?

3 2

[math-fun] Why is there more matter than antimatter?
by Warren D Smith 26 Feb '15

26 Feb '15

What sounds, on the surface anyhow, like an appealing solution: http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.114.061302 -- Warren D. Smith http://RangeVoting.org <-- add your endorsement (by clicking "endorse" as 1st step)

1 1

[math-fun] Completely off-topic: home color printers ?
by Henry Baker 25 Feb '15

25 Feb '15

I can't find an inexpensive _reliable_ color printer. Part of the problem is that I only need color printing every 3 months or so, at which point the previous (expensive) cartridges have always dried out. As bad as this is, at least replacing the cartridges used to work. The newer ink-jet printers now clog the ink jets themselves, and the entire printer becomes useless. There doesn't appear to be any procedure for removing & cleaning these inkjets. I spent a couple of hours looking for color inkjet printers, and it appears that all of these printers require _gigantic_ amounts of software, none of which I need, and they all want to talk directly over the internet to their manufacturers, which I also refuse to allow. Does anyone here have any suggestions?

4 4

Re: [math-fun] Completely off-topic: home color printers ?
by Hilarie Orman 25 Feb '15

25 Feb '15

I use an Epson printer for photos, and I clean out the cartridge spouts with a pin if I've left them unused for a spell. I've not had the inkjet nozzles clog up, but if I did, I'd use Windex to clean them. You could Google it. Hilarie

1 0

Re: [math-fun] Completely off-topic: home color printers ?
by Henry Baker 25 Feb '15

25 Feb '15

At 12:43 PM 2/25/2015, Bill Gosper wrote: >You should be suspicious when they practically give you the printer to begin with. I'm thinking seriously of taking one of these "gifts", hacking the SW, removing the printing HW bits & using it as a server. It has lots of RAM, a decently fast processor, a fast USB port, Ethernet & builtin wifi. Once it runs a version of Linux, it should be a nice server! The Internet-Of-Things, indeed!

1 0

[math-fun] Besides verbify,
by Bill Gosper 24 Feb '15

24 Feb '15

what's another autological verb? SPOILER (white font) neologize --rwg

3 2

[math-fun] Snuggling steinmetzes wrapup(?)
by Bill Gosper 23 Feb '15

23 Feb '15

NeilB's typically expert graphics: gosper.org/steinmetz-diffuse.png gosper.org/steinmetz-glossy.png And a spherical neighborhood of the smothered corner: http://gosper.org/steincorn.png Privately, Dan admitted this was news to him too. I.e., his solid angle question wasn't slyly Socratizing us. --rwg

1 0

[math-fun] test message -- ignore it
by rcs＠xmission.com 23 Feb '15

23 Feb '15

This is a test message. --Rich

1 0