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 A160143 a(n) = Numerator((-1)^n*Euler(2*n)*(2*n+1)/(4^(2*n+1)-2^(2*n+1))), where Euler(n) = A122045(n). 3
 1, 3, 25, 427, 12465, 555731, 35135945, 2990414715, 329655706465, 45692713833379, 1111113564712575, 1595024111042171723, 387863354088927172625, 110350957750914345093747 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Resembles the coefficients of the series for x/cos(x). The first difference with sequence A009843 (expansion of x/cos(x)) occurs at a(10). An explanation can be found in the similarity of the numerators of (2*n+1)/(2^(2*n+1)-1) and the odd numbers 2n+1 (cf. A160144). Similarly, A156769 resembles A036279 (from the expansion of tan(x)). LINKS MAPLE a := n -> (-1)^iquo(n, 2)*euler(n)*(n+1)/(4^(n+1)-2^(n+1)); seq(numer(a(2*n)), n=0..13); CROSSREFS Cf. A009843, A122045, A160144, A160145, A036279, A156769. Sequence in context: A245309 A074708 A323217 * A009843 A182962 A223076 Adjacent sequences:  A160140 A160141 A160142 * A160144 A160145 A160146 KEYWORD frac,nonn AUTHOR Peter Luschny, May 03 2009 STATUS approved

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Last modified May 23 23:00 EDT 2022. Contains 353993 sequences. (Running on oeis4.)