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A102926 Smallest prime factor in product of previous terms +1 or -1. 2
2, 3, 5, 29, 11, 7, 13, 37, 17, 79, 23, 4129, 193, 2593, 101, 19, 39163, 577, 26431, 131, 308798542881428667318174028327605372989, 103, 163, 179, 293, 127, 6287, 683437, 31, 89, 13590243019242466336587034391, 113, 2207, 59, 109, 223, 2351 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
A variant of the Euclid-Mullin construction.
This sequence is listed on the OEIS wiki page "OEIS sequences needing factors" and on the corresponding thread on mersenneforum.org. - M. F. Hasler, Mar 21 2013
LINKS
FORMULA
a(n) = least prime factor of b(n)^2-1, where b(n) = product a(k), 0<k<n, = A102927.
EXAMPLE
a(5)=11 because 2*3*5*29=870, 869=11*79, 871=13*67.
a(31) = 13590243019242466336587034391 because this is the least prime factor of A102927(30)+1. The least prime factor of A102927(30)-1 is 44989026625856465412069667987. Remarkably, both are 29-digit numbers. - David Wasserman, Apr 15 2008
MATHEMATICA
spf[{p_, a_}]:=With[{f=FactorInteger[p^2-1][[1, 1]]}, {p*f, f}]; NestList[ spf, {2, 2}, 36][[All, 2]] (* Harvey P. Dale, May 05 2018 *)
CROSSREFS
Sequence in context: A178376 A041585 A042935 * A084598 A215307 A215103
KEYWORD
nonn
AUTHOR
Marc LeBrun, Jan 19 2005
EXTENSIONS
More terms from Don Reble, Jan 23 2005, corrected Sep 26 2006
Further terms from David Wasserman, Apr 15 2008
STATUS
approved

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Last modified March 28 04:05 EDT 2024. Contains 371235 sequences. (Running on oeis4.)