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 A258091 Smallest prime factor of 1+78557*2^n, cf. A258073. 5
 5, 3, 73, 3, 5, 3, 7, 3, 5, 3, 13, 3, 5, 3, 19, 3, 5, 3, 7, 3, 5, 3, 13, 3, 5, 3, 37, 3, 5, 3, 7, 3, 5, 3, 13, 3, 5, 3, 71, 3, 5, 3, 7, 3, 5, 3, 13, 3, 5, 3, 19, 3, 5, 3, 7, 3, 5, 3, 13, 3, 5, 3, 37, 3, 5, 3, 7, 3, 5, 3, 13, 3, 5, 3, 73, 3, 5, 3, 7, 3, 5, 3 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS a(n) = A020639(A258073(a(n))); a(n) <= 73; see also A258095. Periodic, a(n) = a(n + 840420) for all n (and 840420 is minimal with this property). The only values that occur, are {3, 5, 7, 13, 19, 37, 73} union {47, 59, 71}. - Jeppe Stig Nielsen, Jul 19 2020 LINKS Reinhard Zumkeller, Table of n, a(n) for n = 1..10000 Wikipedia, Sierpinski Number PROG (Haskell) a258091 = a020639 . a258073 (PARI) a(n)=forprime(p=2, , 78557*Mod(2, p)^n+1==0 && return(p)) \\ Jeppe Stig Nielsen, Jul 19 2020 CROSSREFS Cf. A020639, A258073, A258095. Sequence in context: A007299 A257935 A109254 * A255599 A145985 A180403 Adjacent sequences:  A258088 A258089 A258090 * A258092 A258093 A258094 KEYWORD nonn,easy AUTHOR Reinhard Zumkeller, May 19 2015 STATUS approved

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Last modified July 29 17:41 EDT 2021. Contains 346346 sequences. (Running on oeis4.)