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 A160143 A "look-alike" of the coefficients of the series for x/cos(x). 2
 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 The first difference with sequence A009843 (expansion of x/cos(x)) occurs at a(10). An explanation can be found in the "look-alike" of the numerators of (2*n+1)/(4^(2*n+1)-2^(2*n+1)) with the odd numbers 2n+1 (cf. A160144). A156769 describes a similar "look-alike" with A036279 (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, A160144, A160145, A036279, A156769. Sequence in context: A143925 A245309 A074708 * 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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