Largest Known PRP

[science_man_88]

Originally Posted by a1call

I like that reference

http://www.periodictable.com/Samples/026.55/s13.JPG


You know what they say:

You can't teach an old d d d distinguished gentleman new tricks.


PFGW, at the moment is nothing but an acronym to me.
I will have to research it.
Thank you.

it's used on this forum a lot or was at one point, so this forum may help your research if you know how to properly search.

[a1call]

Originally Posted by science_man_88

it's used on this forum a lot or was at one point, so this forum may help your research if you know how to properly search.

Well, I downloaded the linux version from sourceforge. But I can't make it executable on ubuntu because it does not give me root privileges. I wished they would change this unnecessary "security" feature/headache.
But that's fine.

All this is just sort of a hobby.

Thanks anyways.

[Dubslow]

Originally Posted by a1call

Well, I downloaded the linux version from sourceforge. But I can't make it executable on ubuntu because it does not give me root privileges. I wished they would change this unnecessary "security" feature/headache.
But that's fine.

All this is just sort of a hobby.

Thanks anyways.

You don't need root permission to mark-executable a file you downloaded. And if you installed then OS, then you do have root privileges anyways.

[a1call]

I don't think I need to worry about low probability of hitting large PRP.
My Lehrmer non primality code freezes my desktop with 11-dd candidates.

[a1call]

Originally Posted by Dubslow

You don't need root permission to mark-executable a file you downloaded. And if you installed then OS, then you do have root privileges anyways.

In ubuntu:
There is root privileges using su, but I'm a very poor typer and don't know the terminal commands. Looking them up is too much of a hassle.

There is the gksudo for GUIs but running gksudo nautilus only gives you read access to files. you can not change permissions or owners.

All this would be non issue if you could log in as root, which is virtually impossible in ubuntu. There is a large compilation of users requesting this feature over many years, but apparently ubuntu knows better than all of it's incompetent user-base.

On my system anything downloaded is owned by root and I can not make any changes to them.

[GP2]

Originally Posted by a1call

On my system anything downloaded is owned by root and I can not make any changes to them.

There are many systems where you can't log in as root, but you can prefix commands with "sudo" to run that command as root.


Try the following:

If the filename is called "foo", you can make the file executable:

sudo chmod +x foo

You can also change the ownership of the file from root to you:

sudo chown $(whoami) foo

[a1call]

Acknowledged with thanks GP2.

I'm done for the day.
Will give that a try tomorrow eve.

[Dubslow]

Originally Posted by a1call

In ubuntu:
There is root privileges using su, but I'm a very poor typer and don't know the terminal commands. Looking them up is too much of a hassle.

Never use su, use sudo, as explained above.

Originally Posted by a1call

There is the gksudo for GUIs but running gksudo nautilus only gives you read access to files. you can not change permissions or owners.

I'm not too sure about GUIs anymore, but any time you try to something you don't have permissions for, it should give you the popup in which you can type your password. This *should* include things like permissions or owners or whatever, but IDK.

Originally Posted by a1call

All this would be non issue if you could log in as root, which is virtually impossible in ubuntu. There is a large compilation of users requesting this feature over many years, but apparently ubuntu knows better than all of it's incompetent user-base.

Just because the root user does not exist by default (which is a perfectly sensible decision) does *not* mean that you can't do things as root (sudo) or that you can't create the account yourself. (It's one command. Google it if you must, but if you haven't already figured it out, perhaps that's a sign you shouldn't be mucking around with the root account anyways.)

Originally Posted by a1call

On my system anything downloaded is owned by root and I can not make any changes to them.

That's a serious security issue. Anything you download is necessarily owned by the user which ran the browser, and if your browser is running as root, you have way more and worse problems than "I can't change my downloads' permissions" -- your computer thus can be (and possibly is) owned, most literally, by anyone on the internet, with sufficiently malicious javascript. I find it difficult to accept this assertion at face value.

[CRGreathouse]

Originally Posted by a1call

On my system anything downloaded is owned by root and I can not make any changes to them.

Originally Posted by Dubslow

That's a serious security issue. Anything you download is necessarily owned by the user which ran the browser, and if your browser is running as root, you have way more and worse problems than "I can't change my downloads' permissions" -- your computer thus can be (and possibly is) owned, most literally, by anyone on the internet, with sufficiently malicious javascript. I find it difficult to accept this assertion at face value.

Yes. If true that's horrifying (and you need to change things ASAP).

[a1call]

Well I gave all the recommendations a try. no errors, but also no change.

I should add that my ubuntu is a virtual machine that might be the cause problem. The setup is a default setup, so the behavior must be common to any other default virtual machine ubuntu.

Thanks for all the replies.

[LaurV]

Originally Posted by a1call

What is the largest practical p for which
2^(p- 1) can be calculated?

That is limited by the memory of your computer to store it. Just clear all your memory (set all bits to zero) then set the last bit of your memory to 1, and there you are. It takes less than a second.

On a less joking note, here on this very forum the people found the smallest probable prime with at least a million digits. So, one of the largest PRPs we know and don't know if it is prime, has at least a million digits. This is "general form", i.e. nothing "special" about it.

If you go in the "trivia" territory, any mersenne number with a prime exponent is 2-prp, and even strong prp (easy to compute), so the largest "trivial" Poulet/Sarrus numbers we know is 2^M74207281-1. You can't find a bigger one right now...