login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A175257 a(n) is the smallest prime p such that 2^(p-1) == 1 (mod a(1)*...*a(n-1)*p). 1
3, 5, 13, 37, 73, 109, 181, 541, 1621, 4861, 9721, 19441, 58321, 87481, 379081, 408241, 2041201, 2449441, 7348321, 14696641, 22044961, 95528161, 382112641, 2292675841, 8024365441, 40121827201, 481461926401 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
Conjecture: a(n) is the smallest integer k > 1 such that 2^(k-1) == 1 (mod a(0)*...*a(n-1)*k), with a(0) = 1. - Thomas Ordowski, Mar 13 2019
LINKS
MATHEMATICA
i=1; Do[p=Prime[n]; If[Mod[2^(p-1)-1, p*i]==0, Print[p]; i=p*i], {n, 2, 78498}]
PROG
(PARI) findprime(prd) = {forprime(p=2, , if (Mod(2, p*prd)^(p-1) == 1, return (p)); ); }
lista(nn) = {my(prd = 1, na); for (n=1, nn, na = findprime(prd); print1(na, ", "); prd *= na; ); } \\ Michel Marcus, Mar 14 2019
CROSSREFS
Sequence in context: A360863 A005383 A306826 * A190423 A278024 A198636
KEYWORD
more,nonn
AUTHOR
Manuel Valdivia, Mar 15 2010
EXTENSIONS
a(17)-a(26) from Amiram Eldar, Feb 03 2019
Name corrected by Thomas Ordowski, Mar 13 2019
a(27) from Hans Havermann, Mar 29 2019
Eliminated a(0)=1 in the definition (empty products equal 1). - R. J. Mathar, Jun 19 2021
STATUS
approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified March 28 08:02 EDT 2024. Contains 371236 sequences. (Running on oeis4.)