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A175257 a(n) is the smallest prime p such that 2^(p-1) == 1 (mod a(0)*...*a(n-1)*p), with a(0) = 1. 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

Table of n, a(n) for n=1..27.

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

Cf. A007663, A096060, A002200, A005109, A306826.

Sequence in context: A032027 A005383 A306826 * A190423 A278024 A198636

Adjacent sequences:  A175254 A175255 A175256 * A175258 A175259 A175260

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

STATUS

approved

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Last modified August 7 06:02 EDT 2020. Contains 336274 sequences. (Running on oeis4.)