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 A256020 a(n) = Sum_{i=1..n-1} (i^4 * a(i)), a(1)=1. 2
 1, 1, 17, 1394, 358258, 224269508, 290877551876, 698687879606152, 2862524242746404744, 18783884080901907930128, 187857624693099981209210128, 2750611340756369924865254694176, 57039427373264843131930786593127712, 1629160124635190449534207126672913710144 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 LINKS FORMULA Product_{i=2..n-1} (i^4 + 1), for n>2. a(n) ~ (cosh(Pi/sqrt(2))^2 * sin(Pi/sqrt(2))^2 + cos(Pi/sqrt(2))^2 * sinh(Pi/sqrt(2))^2) / (2*Pi^2) * ((n-1)!)^4. a(n) = A255434(n-1)/2. MATHEMATICA Clear[a]; a[1]=1; a[n_]:= a[n] = Sum[i^4*a[i], {i, 1, n-1}]; Table[a[n], {n, 1, 15}] Flatten[{1, 1, Table[Product[(i^4 + 1), {i, 2, n-1}], {n, 3, 15}]}] Join[{1}, FoldList[Times, Range[15]^4+1]/2] (* Harvey P. Dale, Jul 29 2018 *) CROSSREFS Cf. A001710, A051893, A256019. Sequence in context: A007410 A203229 A269791 * A072160 A078814 A242282 Adjacent sequences:  A256017 A256018 A256019 * A256021 A256022 A256023 KEYWORD nonn AUTHOR Vaclav Kotesovec, Mar 13 2015 STATUS approved

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Last modified August 3 17:26 EDT 2020. Contains 336200 sequences. (Running on oeis4.)