Timeline for Can exist a positive integer number $x$ such that $a_1=x$ and $a_n=2a_{n-1}+1$ are not prime for all $n \ge 1$?
Current License: CC BY-SA 4.0
8 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Jul 4 at 10:57 | answer | added | Gerry Myerson | timeline score: 9 | |
| Jul 3 at 12:59 | comment | added | Dieter Kadelka | According to the link in Wojowu's comment it still seems open to determine the smallest Riesel number. | |
| Jul 3 at 12:51 | comment | added | Wojowu | Per Dieter's comment, these are precisely $x$ such that $x+1$ is a Riesel number. | |
| Jul 3 at 12:10 | comment | added | Đào Thanh Oai | @ClaudeChaunier Thanks you very much. Maybe my program fail or not accuracy. | |
| Jul 3 at 11:57 | comment | added | Claude Chaunier | In the OP example $x=490$, it is true that $a_n$ is not prime for $n\le 46$, however $a_{47} = 34551053391233023$ is prime, according to GP/PARI isprime function. | |
| Jul 3 at 11:00 | answer | added | David E Speyer | timeline score: 18 | |
| Jul 3 at 10:26 | comment | added | Dieter Kadelka | Note that $a_n = (x+1)*2^{n-1} - 1$. | |
| Jul 3 at 9:52 | history | asked | Đào Thanh Oai | CC BY-SA 4.0 |