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A129768
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Number of odd nonprime numbers less than the n-th prime.
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1
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1, 1, 1, 1, 2, 2, 3, 3, 4, 6, 6, 8, 9, 9, 10, 12, 14, 14, 16, 17, 17, 19, 20, 22, 25, 26, 26, 27, 27, 28, 34, 35, 37, 37, 41, 41, 43, 45, 46, 48, 50, 50, 54, 54, 55, 55, 60, 65, 66, 66, 67, 69, 69, 73, 75, 77, 79, 79, 81, 82, 82, 86, 92, 93, 93, 94, 100, 102, 106, 106, 107, 109
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OFFSET
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1,5
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COMMENTS
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Also, a(n)=sum_{k=n-th even number..n-th odd prime together with 1}-k*(-1)^k. - Juri-Stepan Gerasimov, Jul 30 2009
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LINKS
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FORMULA
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MAPLE
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A129768 := proc(n) local res, p, i ; res := 0 ; p := ithprime(n) ; for i from 1 to p-1 by 2 do if not isprime(i) then res := res+1 ; fi ; od ; RETURN(res) ; end: for n from 1 to 80 do printf("%d, ", A129768(n)) ; od ; # R. J. Mathar, May 17 2007
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MATHEMATICA
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nn=401; With[{np=Select[Range[1, nn, 2], !PrimeQ[#]&]}, Table[Count[np, _?(#<n&)], {n, Prime[Range[PrimePi[nn]]]}]] (* Harvey P. Dale, Mar 01 2015 *)
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CROSSREFS
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KEYWORD
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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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