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A121884
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Excess of n-th semiprime over previous prime.
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1
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1, 1, 2, 3, 1, 2, 2, 3, 2, 3, 2, 3, 4, 1, 2, 3, 2, 4, 2, 4, 5, 1, 4, 2, 1, 4, 3, 2, 3, 4, 2, 4, 5, 6, 3, 2, 2, 5, 6, 8, 9, 10, 2, 2, 3, 2, 3, 4, 6, 7, 4, 1, 2, 4, 3, 2, 4, 5, 2, 4, 6, 1, 2, 3, 4, 6, 7, 10, 2, 3, 4, 6, 7, 8, 10, 3, 2, 4, 6, 8, 2, 3, 2, 5, 2, 4, 3, 1, 4, 6, 8, 2, 5, 6, 8, 9, 10, 12, 2, 1, 2, 4, 6
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,3
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COMMENTS
| a(n) = 1 iff n is in A077068. a(n) = 2 iff n is in A062721.
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LINKS
| Robert G. Wilson, v, Table of n, a(n) for n=1..1000.<br>
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FORMULA
| a(n) = Min{A001358(n)-p for p < A001358(n) and p in A000040(k)}.
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MATHEMATICA
| semiPrimeQ[n_] := Plus @@ Last /@ FactorInteger[n] == 2; lst1 = Select[ Range@ 325, semiPrimeQ@# &]; lst = Select[ Range@ 500, semiPrimeQ@# &]; lst - (NextPrime[ #, -1] & /@ lst) [From Robert G. Wilson v (rgwv(AT)rgwv.com), Mar 16 2009]
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CROSSREFS
| Cf. A000040, A001358, A062721, A077068.
Sequence in context: A106798 A194298 A194306 * A079087 A205003 A159956
Adjacent sequences: A121881 A121882 A121883 * A121885 A121886 A121887
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KEYWORD
| easy,nonn
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AUTHOR
| Jonathan Vos Post (jvospost3(AT)gmail.com), Aug 31 2006
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EXTENSIONS
| a(31)-a(103) from Robert G. Wilson v (rgwv(AT)rgwv.com), Mar 16 2009
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