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 A331338 E.g.f.: Sum_{k>=1} (1 - sech(x^k)) (even powers only). 0
 1, 7, 421, 10375, 1864921, 177588115, 43788506581, 5364386887855, 3746015060385841, 743097477083711275, 562069712763196977901, 208700966175150043937095, 201649817635812110915892361, 89621739407126401163202051715, 158792595367325562826629059282821 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS FORMULA a(n) = -(2*n)! * Sum_{d|n} A028296(d) / (2*d)!. MATHEMATICA nmax = 15; Table[(CoefficientList[Series[Sum[1 - Sech[x^k], {k, 1, nmax}], {x, 0, 2 nmax}], x] Range[0, 2 nmax]!)[[n]], {n, 1, 2 nmax + 1, 2}] // Rest Table[-(2 n)! DivisorSum[n, EulerE[2 #]/(2 #)! &], {n, 1, 15}] CROSSREFS Cf. A000364, A028296, A176474, A330255, A330528. Sequence in context: A286393 A099742 A287033 * A269555 A027876 A158599 Adjacent sequences:  A331335 A331336 A331337 * A331339 A331340 A331341 KEYWORD nonn AUTHOR Ilya Gutkovskiy, Jan 14 2020 STATUS approved

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Last modified September 24 04:42 EDT 2020. Contains 337317 sequences. (Running on oeis4.)