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A119965
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The 3-almost primeth recurrence: a(0) = 1, a(n+1) = 3-almostprime(a(n)) = A014612(a(n)).
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1
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1, 8, 42, 174, 705, 2764, 10772, 41967, 164793, 654242, 2634801, 10787937, 44983894, 191249703, 829651874, 3673967785, 16612478231, 76708135651, 361707435767, 1741601413569, 8561660600005
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,2
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COMMENTS
| 3-almostprime equivalent of Wilson's primeth recurrence: A007097.
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MATHEMATICA
| ThreeAlmostPrimePi[n_] := Sum[PrimePi[n/(Prime@i*Prime@j)] - j + 1, {i, PrimePi[n^(1/3)]}, {j, i, PrimePi@Sqrt[n/Prime@i]}]; ThreeAlmostPrime[n_] := Block[{e = Floor[Log[2, n] + 1], a, b}, a = 2^e; Do[b = 2^p; While[ThreeAlmostPrimePi[a] < n, a = a + b]; a = a - b/2, {p, e, 0, -1}]; a + b/2]; NestList[ThreeAlmostPrime@# &, 1, 18]
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CROSSREFS
| Cf. A007097, A105999, A119966.
Sequence in context: A204572 A086392 A027903 * A055082 A093381 A097788
Adjacent sequences: A119962 A119963 A119964 * A119966 A119967 A119968
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KEYWORD
| nonn
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AUTHOR
| Jonathan Vos Post (jvospost3(AT)gmail.com) and Robert G. Wilson v (rgwv(AT)rgwv.com), May 31 2006
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EXTENSIONS
| a(19)-a(20) from Donovan Johnson (donovan.johnson(AT)yahoo.com), Sep 29 2010
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