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A116922
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a(n) = smallest integer >= n/2 which is coprime to n.
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3
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1, 1, 2, 3, 3, 5, 4, 5, 5, 7, 6, 7, 7, 9, 8, 9, 9, 11, 10, 11, 11, 13, 12, 13, 13, 15, 14, 15, 15, 17, 16, 17, 17, 19, 18, 19, 19, 21, 20, 21, 21, 23, 22, 23, 23, 25, 24, 25, 25, 27, 26, 27, 27, 29, 28, 29, 29, 31, 30, 31, 31, 33, 32, 33, 33, 35, 34, 35, 35, 37, 36, 37, 37, 39, 38
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OFFSET
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1,3
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COMMENTS
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For n>= 3, a(n) - A116921(n) is 1 if n is odd, is 2 if n is a multiple of 4 and is 4 if n is congruent to 2 (mod 4).
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LINKS
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FORMULA
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For n >= 3, a(n) = (n+1)/2 if n is odd, a(n) = n/2 + 1 if n is a multiple of 4 and a(n) = n/2 + 2 if n is congruent to 2 (mod 4).
G.f.: t*(1 + t^2 + t^3 - t^4 + 2*t^5 - 2*t^6)/((1-t)*(1-t^4)). - Mamuka Jibladze, Aug 22 2019
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MATHEMATICA
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cp[n_]:=Module[{k=Ceiling[n/2]}, While[!CoprimeQ[n, k], k++]; k]; Array[cp, 80] (* Harvey P. Dale, Nov 06 2013 *)
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PROG
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(PARI) a(n) = {if(n%2, (n+1)/2, if(n==2, 1, n/2 + if(n%4, 2, 1)))} \\ Andrew Howroyd, Aug 22 2019
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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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More terms from Wyatt Lloyd (wal118(AT)psu.edu), Mar 25 2006
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STATUS
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approved
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