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Search: id:A102084
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| A102084 |
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a(0) = 0; for n>0, write 2n=p+q (p, q prime), p*q maximal; then a(n)=p*q (see A073046). |
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| 0, 4, 9, 15, 25, 35, 49, 55, 77, 91, 121, 143, 169, 187, 221, 247, 289, 323, 361, 391, 437, 403, 529, 551, 589, 667, 713, 703, 841, 899, 961, 943, 1073, 1147, 1189, 1271, 1369, 1363, 1517, 1591, 1681, 1763, 1849, 1927, 2021, 1891, 2209, 2279, 2257, 2491
(list; graph; listen)
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OFFSET
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2,2
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COMMENT
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For n>0, largest semiprime whose sum of prime factors = 2n.
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EXAMPLE
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n=13: 2n=26; 26=23+3=19+7=13+13; 13*13=maximal=>p*q=13*13=169
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MATHEMATICA
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f[n_] := Block[{pf = FactorInteger[n]}, If[Plus @@ Last /@ pf == 2, If[ Length[pf] == 2, Plus @@ First /@ pf, 2pf[[1, 1]]], 0]]; t = Table[0, {51}]; Do[a = f[n]; If[ EvenQ[a] && 0 < a < 104, t[[a/2]] = n], {n, 2540}]; t (from Robert G. Wilson v (rgwv(AT)rgwv.com), Jun 14 2005)
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CROSSREFS
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Cf. A073046.
Sequence in context: A109641 A134675 A050530 this_sequence A030664 A070160 A056928
Adjacent sequences: A102081 A102082 A102083 this_sequence A102085 A102086 A102087
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KEYWORD
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nonn
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AUTHOR
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Michael Taktikos (michael.taktikos(AT)hanse.net), Feb 16 2005
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EXTENSIONS
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Edited by N. J. A. Sloane (njas(AT)research.att.com), Aug 29 2008 at the suggestion of R. J. Mathar
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