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 A128060 a(n) = 2*n - numerator((2*n-1)^2/(2*(2*n)!)). 4
 -1, 1, 1, 1, 1, 9, 1, 1, 15, 1, 1, 21, 1, 25, 27, 1, 1, 33, 35, 1, 39, 1, 1, 45, 1, 49, 51, 1, 55, 57, 1, 1, 63, 65, 1, 69, 1, 1, 75, 77, 1, 81, 1, 85, 87, 1, 91, 93, 95, 1, 99, 1, 1, 105, 1, 1, 111, 1, 115, 117, 119, 121, 123 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,6 COMMENTS Odd composite numbers with placeholders for primes between them. LINKS FORMULA a(n) = 2*n - A128059(n) a(n) = (A217983(n-1) * (2*n-1))/A160479(n) for n >= 3. [Johannes W. Meijer, Oct 25 2012] a(0) = -1, a(n) = GCD(2n-1, (2n-2)!), n > 0. - Wesley Ivan Hurt, Jan 05 2014 MAPLE A128060 := proc(n): 2*n - numer((2*n-1)^2/(2*(2*n)!)) end: seq(A128060(n), n=0..62); # End program 1 [Johannes W. Meijer, Oct 25 2012] A128060 := proc(n) local n1: n1:=2*n-1: if type(n1, prime) then A128060(n) := 1 else A128060(n) := n1 fi: end: seq(A128060(n), n=0..62); # End program 2 [Johannes W. Meijer, Oct 25 2012] MATHEMATICA Table[2n - Numerator[(2n - 1)^2/(2(2n)!)], {n, 0, 74}] (* Alonso del Arte, Jan 05 2014 *) CROSSREFS Sequence in context: A195703 A174948 A092578 * A168625 A143681 A081582 Adjacent sequences:  A128057 A128058 A128059 * A128061 A128062 A128063 KEYWORD easy,sign AUTHOR Paul Barry, Feb 13 2007 STATUS approved

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