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A121885
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Excess of n-th prime over previous semiprime.
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2
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1, 1, 1, 3, 2, 4, 1, 3, 5, 2, 2, 4, 1, 2, 1, 3, 2, 2, 4, 2, 1, 2, 2, 6, 8, 1, 3, 2, 4, 2, 3, 5, 3, 5, 2, 2, 1, 4, 1, 3, 4, 6, 3, 5, 2, 2, 1, 3, 7, 2, 4, 2, 3, 1, 2, 4, 3, 3, 5, 2, 2, 2, 4, 3, 2, 2, 1, 3, 7, 1, 2, 2, 2, 1, 3, 2, 3, 2, 2, 4, 4, 6, 2, 6, 2, 3, 3
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OFFSET
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3,4
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COMMENTS
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See: A102415 Greatest semiprime less than n-th prime. See: A102414 Smallest semiprime greater than n-th prime.
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LINKS
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FORMULA
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MATHEMATICA
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SemiPrimeQ[n_Integer] := If[Abs[n] < 2, False, (2 == Plus @@ Transpose[FactorInteger[Abs[n]]][[2]])]; Table[i = Prime[n] - 1; While[! SemiPrimeQ[i], i--]; Prime[n] - i, {n, 3, 100}] (* T. D. Noe, Oct 08 2012 *)
eps[n_]:=Module[{c=n-1}, While[PrimeOmega[c]!=2, c--]; n-c]; Table[eps[n], {n, Prime[Range[3, 90]]}] (* Harvey P. Dale, Aug 12 2014 *)
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PROG
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(PARI) dsemi(n)= { local(k=0); if(isprime(n), k=0; while(bigomega(n-k)<>2&&k<n, k=k+1)); return(k) }
{ forprime(n=5, 10^3, print(n, " ", dsemi(n))) } // Antonio Roldán, Oct 08 2012
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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