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 A034970 a(n) is the greatest prime factor of a(n-2)*a(n-1)-1. 2
 2, 3, 5, 7, 17, 59, 167, 821, 2539, 1042259, 508903, 5765312303, 1461701, 1404527126434567, 2034580216153, 97552206663238517, 3105563257, 46137561830961960349, 9777395920402541, 6719860896292085951563127, 5367788603966004659, 33011914147 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 LINKS Sami Liedes, Table of n, a(n) for n = 0..34 MAPLE with(numtheory): a:= proc(n) option remember; `if`(n<2, n+2,       max(factorset(a(n-2)*a(n-1)-1)[]))     end: seq(a(n), n=0..22);  # Alois P. Heinz, Feb 03 2014 MATHEMATICA a[0] = 2; a[1] = 3; a[n_] := a[n] = FactorInteger[ a[n-2]*a[n-1] - 1][[-1, 1]]; Table[a[n], {n, 0, 21}] (* Jean-François Alcover, Mar 09 2012 *) nxt[{a_, b_}]:={b, FactorInteger[a*b-1][[-1, 1]]}; Transpose[NestList[nxt, {2, 3}, 25]][[1]] (* Harvey P. Dale, Apr 05 2014 *) PROG (PARI) A034970(a, b) = {local(f); f=factor(a*b-1); f[matsize(f)[1], 1]} a=2; b=3; print(a); print(b) for(n=2, 28, c=A034970(a, b); print(c); a=b; b=c) (Haskell) a034970 n = a034970_list !! n a034970_list = 2 : 3 : (map (a006530 . (subtract 1)) \$                         zipWith (*) a034970_list \$ tail a034970_list) -- Reinhard Zumkeller, Feb 23 2012 CROSSREFS Cf. A006530, A031441. Sequence in context: A231480 A040149 A168034 * A048417 A071710 A048403 Adjacent sequences:  A034967 A034968 A034969 * A034971 A034972 A034973 KEYWORD nonn,easy,nice AUTHOR EXTENSIONS More terms from James A. Sellers Terms corrected by Michael B. Porter, Mar 14 2010 STATUS approved

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Last modified January 17 10:08 EST 2019. Contains 319218 sequences. (Running on oeis4.)