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 A248049 a(n) = (a(n-1) + a(n-2)) * (a(n-2) + a(n-3)) / a(n-4) with a(0) = 2, a(1) = a(2) = a(3) = 1. 2
 2, 1, 1, 1, 2, 6, 24, 240, 3960, 184800, 33033000, 26125799700, 219429008298500, 31064340573760168675, 206377779224083011749949745, 245390990689739612867279321757020455, 230795626149641527446533813473152766756062242744 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS It seems that degrees of factors when using [2,1,1,y] as initial condition are given by A233522. - F. Chapoton, May 21 2020 It seems also that degrees (w.r.t. x) of factors when using [2,1,x,y] as initial condition are given by A247907. - F. Chapoton, Jan 03 2021 Somos conjectures that log(a(n)) ~ 1.25255*c^n, where c = A060006. - Bill McEachen, Oct 11 2022 LINKS Robert Israel, Table of n, a(n) for n = 0..26 Math Stack Exchange, Is OEIS A248049 an Integer Sequence FORMULA a(n) = a(4-n) for all n in Z. a(n) * a(n+4) = (a(n+1) + a(n+2)) * (a(n+2) + a(n+3)) for all n in Z. MAPLE a[0]:= 2: a[1]:= 1: a[2]:= 1: a[3]:= 1: for n from 4 to 20 do a[n] := (a[n-1] + a[n-2]) * (a[n-2] + a[n-3]) / a[n-4] od: seq(a[i], i=0..20); # Robert Israel, Mar 18 2020 PROG (PARI) {a(n) = if( n<0, n=4-n); if( n<4, (n==0)+1, (a(n-1) + a(n-2)) * (a(n-2) + a(n-3)) / a(n-4))}; CROSSREFS Cf. A233522, A060006. Sequence in context: A179272 A264753 A165680 * A231867 A105685 A228239 Adjacent sequences: A248046 A248047 A248048 * A248050 A248051 A248052 KEYWORD nonn AUTHOR Michael Somos, Sep 30 2014 STATUS approved

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Last modified December 2 09:21 EST 2023. Contains 367516 sequences. (Running on oeis4.)