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 A190351 Define a series of lists by L_1 = [1], L_{k+1} = [i+1, i^2+i+1 : i in L_k]; then a(n) = denominator of Sum (1/i : i in L_n). 1
 1, 6, 1092, 4218760, 27765973216255750329906360, 229254309739144896253372216696442967123093789661296276592384463520 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Sum (1/i : i in L_n) converges to Pi/4 as n -> oo. REFERENCES J. Borwein, D. Bailey and R. Girgensohn, Experimentation in Mathematics: Computational Paths to Discovery, Peters, Boston, 2004. See Sect. 1.3. LINKS EXAMPLE 1, 5/6, 877/1092, 3349607/4218760, 21942759935479332971926241/27765973216255750329906360, ... MAPLE M:=6; s1:={1}; n1[1]:=1; for n from 2 to M do s2:={}; for i in s1 do s2:={op(s2), i+1, i^2+i+1 }; od: n1[n] := add(1/i, i in s2): s1:=s2; od: s3:=[seq(n1[i], i=1..M)]; CROSSREFS Cf. A190350. Sequence in context: A003763 A179853 A268043 * A267071 A219165 A185537 Adjacent sequences:  A190348 A190349 A190350 * A190352 A190353 A190354 KEYWORD nonn,frac AUTHOR N. J. A. Sloane, May 09 2011 STATUS approved

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Last modified May 27 16:48 EDT 2022. Contains 354110 sequences. (Running on oeis4.)