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URL: https://oeis.org/A242064

⇱ A242064 - OEIS

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A242064
Smallest k such that the union of {A242033(i): 1 <= i <= k} and {A242034(i): 1 <= i <= k} includes all primes {3, ..., prime(n)}.
3
1, 2, 9, 9, 36, 36, 81, 220, 220, 386, 386, 386, 434, 521, 896, 896, 896, 1167, 1167, 1695, 2065, 2096, 2096, 2968, 2968, 2968, 2968, 3341, 4561, 4561, 4561, 4561, 4672, 4672, 5964, 6203, 7158, 8294, 8294, 8294, 8740, 8740, 10452, 10452, 11075, 11075, 12092
OFFSET
2,2
MATHEMATICA
lpf[n_]:=lpf[n]=First[First[FactorInteger[n]]]; (*least prime factor*)
A242033=Map[lpf[#-1]&, Select[Range[6, 100000, 2], lpf[#-1]<lpf[#-3]&](*A245024*)];
A242034=Map[lpf[#-3]&, Select[Range[6, 100000, 2], lpf[#-1]>lpf[#-3]&](*A243937*)];
pos={}; NestWhile[#+1&, 2, (AppendTo[pos, Min[Position[A242033, Prime[#], 1, 1], Position[A242034, Prime[#], 1, 1]/.{}->0]]; !Last[pos]==0)&];
A242064=Rest[FoldList[Max, -Infinity, Flatten[pos]]] (* Peter J. C. Moses, Aug 14 2014 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Vladimir Shevelev, Aug 13 2014
EXTENSIONS
More terms from Peter J. C. Moses, Aug 14 2014
STATUS
approved