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Search: id:A098026
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| A098026 |
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Smallest prime p such that p+1 has exactly n distinct prime factors. |
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+0
4
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| 2, 5, 29, 389, 2309, 30029, 570569, 11741729, 300690389, 10407767369, 239378649509, 9426343036109, 304250263527209, 19835154277048109, 693386350578511589, 37508276737897976009, 2925030695773453637369
(list; graph; listen)
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OFFSET
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1,1
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EXAMPLE
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a(4) = 389 because 389+1 = 2*3*5*13.
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MATHEMATICA
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Generate[pIndex_, i_] := Module[{p2, t}, p2=pIndex; While[p2[[i]]++; Do[p2[[j]]=p2[[i]]+j-i, {j, i+1, Length[p2]}]; t=Times@@Prime[p2]; t<fact*base, AppendTo[s, t]; If[i<Length[p2], Generate[p2, i+1]]]]; fact=2; Table[pin=Range[n]; base=Times@@Prime[pin]; s={base}; Do[Generate[pin, j], {j, n}]; s=Sort[s]; noPrime=True; i=0; While[noPrime&&i<Length[s], i++; noPrime=!PrimeQ[ -1+s[[i]]]]; If[noPrime, -1, -1+s[[i]]], {n, 20}] (T. D. Noe)
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CROSSREFS
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Cf. A073918 (least prime p such that p-1 has exactly n distinct prime factors).
Sequence in context: A098682 A108367 A103592 this_sequence A064098 A098717 A059784
Adjacent sequences: A098023 A098024 A098025 this_sequence A098027 A098028 A098029
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KEYWORD
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nonn
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AUTHOR
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Lekraj Beedassy (blekraj(AT)yahoo.com), Sep 10 2004
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EXTENSIONS
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Corrected and extended by Ray Chandler (rayjchandler(AT)sbcglobal.net), Sep 18 2004
Further corrected and extended by T. D. Noe (noe(AT)sspectra.com), Dec 13 2004
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