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Search: id:A078846
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| A078846 |
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Where 11^n occurs in n-almost-primes, starting at a(0)=1. |
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15
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| 1, 5, 40, 328, 2556, 18452, 126096, 827901, 5276913, 32887213, 201443165, 1217389949
(list; graph; listen)
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OFFSET
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0,2
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COMMENT
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A k-almost-prime is a positive integer that has exactly k prime factors, counted with multiplicity.
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LINKS
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Eric Weisstein's World of Mathematics, Almost Prime.
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EXAMPLE
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a(2) = 40 since 11^2 is the 40-th 2-almost-prime: A001358(40) = 121.
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MATHEMATICA
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AlmostPrimePi[k_Integer /; k > 1, n_] := Module[{a, i}, a[0] = 1; Sum[PrimePi[n/Times @@ Prime[Array[a, k - 1]]] - a[k - 1] + 1, Evaluate[Sequence @@ Table[{a[i], a[i - 1], PrimePi[(n/Times @@ Prime[Array[a, i - 1]])^(1/(k - i + 1))]}, {i, k - 1}]]]]; Eric Weisstein (eww(AT)wolfram.com) Feb 07 2006
Table[ AlmostPrimePi[n, 11^n], {n, 2, 11}] (* Robert G. Wilson v *)
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CROSSREFS
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Cf. A078840, A078841, A078842, A078843, A078844, A078845.
Sequence in context: A145841 A123943 A067412 this_sequence A027259 A007036 A052798
Adjacent sequences: A078843 A078844 A078845 this_sequence A078847 A078848 A078849
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KEYWORD
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more,nonn
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AUTHOR
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Benoit Cloitre (benoit7848c(AT)orange.fr) and Paul D. Hanna (pauldhanna(AT)juno.com), Dec 10 2002
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EXTENSIONS
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a(6)-a(11) from Robert G. Wilson v (rgwv(at)rgwv.com), Feb 09 2006
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