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A105999
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Semiprimeth recurrence: a(0) = 1, a(n+1) = semiprime(a(n)) = A001358(a(n)).
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6
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1, 4, 10, 26, 77, 235, 779, 2785, 10643, 43697, 192893, 915218, 4657929, 25380749, 147721169, 916036271, 6037442989, 42191467826, 311911160465, 2434014941905, 20007995450483, 172911791611798, 1568190042677867
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,2
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COMMENTS
| Semiprime equivalent of R.G.Wilson's primeth recurrence: A007097.
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EXAMPLE
| a(1) = semiprime(1) = 4.
a(2) = semiprime(semiprime(1)) = semiprime(4) = 10.
a(3) = semiprime(semiprime(semiprime(1))) = semiprime(semiprime(4)) = semiprime(10) = 26.
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MATHEMATICA
| SemiPrimePi[n_] := Sum[PrimePi[n/Prime@i] - i + 1, {i, PrimePi@ Sqrt@n}]; SemiPrime[n_] := Block[{e = Floor[Log[2, n] + 1], a, b}, a = 2^e; Do[b = 2^p; While[SemiPrimePi@a < n, a = a + b]; a = a - b/2, {p, e, 0, -1}]; a + b/2]; NestList[SemiPrime@# &, 1, 18] - from Robert G. Wilson v (rgwv(AT)rgwv.com), May 31 2006
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CROSSREFS
| Cf. A001358, A007097, A091022, A105997, A105998.
Sequence in context: A099234 A087222 A130583 * A192210 A121494 A122744
Adjacent sequences: A105996 A105997 A105998 * A106000 A106001 A106002
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KEYWORD
| nonn
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AUTHOR
| Jonathan Vos Post (jvospost3(AT)gmail.com), Apr 29 2005
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EXTENSIONS
| a(5)-a(15) from Robert G. Wilson v (rgwv(AT)rgwv.com), Apr 30 2005
a(16)-a(20) from Robert G. Wilson v (rgwv(AT)rgwv.com), May 31 2006
a(21)-a(22) from Donovan Johnson (donovan.johnson(AT)yahoo.com), Sep 24 2010
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