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 A031441 a(0) = 3; for n > 0, a(n) is the greatest prime factor of PreviousPrime(a(n-1))*a(n-1)-1 where PreviousPrime(prime(k))=prime(k-1). 5
 3, 5, 7, 17, 11, 19, 23, 109, 17, 11, 19, 23, 109, 17, 11, 19, 23, 109, 17, 11, 19, 23, 109, 17, 11, 19, 23, 109, 17, 11, 19, 23, 109, 17, 11, 19, 23, 109, 17, 11, 19, 23, 109, 17, 11, 19, 23, 109, 17, 11, 19, 23, 109, 17, 11, 19, 23, 109, 17, 11, 19, 23, 109, 17, 11, 19, 23 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 LINKS Harvey P. Dale, Table of n, a(n) for n = 0..1000 EXAMPLE To get a(3) we compute PreviousPrime(7)=5, 5*7-1=34, greatest prime factor of 34 is 17, so a(3)=17. MATHEMATICA a[0] = 3; a[n_] := a[n] = FactorInteger[ NextPrime[ a[n-1], -1]*a[n-1] - 1][[-1, 1]]; Table[a[n], {n, 0, 66}] (* Jean-François Alcover, Mar 09 2012 *) NestList[FactorInteger[NextPrime[#, -1]*#-1][[-1, 1]]&, 3, 70] (* Harvey P. Dale, Dec 13 2012 *) CROSSREFS Cf. A034970, A031442. Sequence in context: A078683 A099863 A112092 * A078150 A276044 A114265 Adjacent sequences:  A031438 A031439 A031440 * A031442 A031443 A031444 KEYWORD nonn,easy,nice AUTHOR EXTENSIONS More terms from James A. Sellers STATUS approved

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Last modified February 28 08:20 EST 2020. Contains 332321 sequences. (Running on oeis4.)