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-   -   Two variable functions (https://www.mersenneforum.org/showthread.php?t=25302)

 enzocreti 2020-02-26 14:35

Two variable functions

223*34^x+5879*y-(y-2)*17^2+10=f(x,y)
23*34^x+5879*y-(y-2)*17^2+10=g(x,y)

I search integers k>0 such that

either

f(x,y)=k

or

g(x,y)=k

have integer solutions x and y greater than 0.

Is it possible to find such k up to 10^6?

 CRGreathouse 2020-02-27 04:52

[QUOTE=enzocreti;538369]Is it possible to find such k up to 10^6?[/QUOTE]

It is! I find 678 such members. You could, too, with my code below and a copy of [url=https://pari.math.u-bordeaux.fr/]PARI/GP[/url]. The parameters are pretty extensible in case you'd like to modify things.

[code]liste(lim,mul,base=34,step=5590,offset=588)=my(v=List(),X=mul*base); lim\=1; while(X<lim,forstep(n=X+offset+step,lim,step, listput(v,n)); X*=base); Set(v)
list(lim)=setunion(liste(lim,23),liste(lim,223))
v=list(1e6)[/code]

Up to a billion I find 1370532 or 0.1%. Asymptotically I think the density is about 1.5% (42/2795) but it will take a while to get there.

 enzocreti 2020-02-27 06:13

[QUOTE=CRGreathouse;538411]It is! I find 678 such members. You could, too, with my code below and a copy of [url=https://pari.math.u-bordeaux.fr/]PARI/GP[/url]. The parameters are pretty extensible in case you'd like to modify things.

[code]liste(lim,mul,base=34,step=5590,offset=588)=my(v=List(),X=mul*base); lim\=1; while(X<lim,forstep(n=X+offset+step,lim,step, listput(v,n)); X*=base); Set(v)
list(lim)=setunion(liste(lim,23),liste(lim,223))
v=list(1e6)[/code]

Up to a billion I find 1370532 or 0.1%. Asymptotically I think the density is about 1.5% (42/2795) but it will take a while to get there.[/QUOTE]

Among the solutions there are k=69660, 92020 and 541456 which are the exponents of pg primes multiple of 86.
Is it a chance?

 CRGreathouse 2020-02-27 07:17

[QUOTE=enzocreti;538415]Among the solutions there are k=69660, 92020 and 541456 which are the exponents of pg primes multiple of 86.
Is it a chance?[/QUOTE]

Probably! You cover a lot of residue classes, and your method isn't clear. Had you specified a method *before* I found the list it would have been more compelling.

 enzocreti 2020-02-27 08:15

...

[QUOTE=CRGreathouse;538419]Probably! You cover a lot of residue classes, and your method isn't clear. Had you specified a method *before* I found the list it would have been more compelling.[/QUOTE]

All the k's (for k multiple of 43) that are solutions if I am not wrong are congruent to (7^3+1) mod 559.
Why?

 enzocreti 2020-02-27 10:01

...

[QUOTE=CRGreathouse;538419]Probably! You cover a lot of residue classes, and your method isn't clear. Had you specified a method *before* I found the list it would have been more compelling.[/QUOTE]

92020, 69660 and 541456 are moreover congruent to 10^m mod 41...

I don't know if there are other k's solutions that are congruent to 10^m mod 41

 CRGreathouse 2020-02-28 02:21

[QUOTE=enzocreti;538433]92020, 69660 and 541456 are moreover congruent to 10^m mod 41...

I don't know if there are other k's solutions that are congruent to 10^m mod 41[/QUOTE]

I mean, znorder(Mod(10,41)) = 5. It's not a rare property.

 enzocreti 2020-02-28 08:50

...

[QUOTE=CRGreathouse;538480]I mean, znorder(Mod(10,41)) = 5. It's not a rare property.[/QUOTE]

yes I don't understand why the k solutions multiple of 43 are all congruent to 344 mod 559

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