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 A121959 a(n) = (n-3)*a(n-1) + a(n-4), with a(1)=0, a(2)=1, a(3)=2, a(4)=3. 1
 0, 1, 2, 3, 6, 19, 78, 393, 2364, 16567, 132614, 1193919, 11941554, 131373661, 1576616546, 20497209017, 286972867792, 4304724390541, 68877166865202, 1170932333917451, 21077068983381910, 400468615408646831 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 LINKS G. C. Greubel, Table of n, a(n) for n = 1..450 MAPLE a:= proc(n) option remember;       if n<5 then n-1     else (n-3)*a(n-1) + a(n-4)       fi;     end: seq(a(n), n=1..30); # G. C. Greubel, Oct 05 2019 MATHEMATICA (* First program *) M = {{0, 1, 0, 0}, {0, 0, 1, 0}, {0, 0, 0, 1}, {1, 0, 0, n}}; v[1] = {0, 1, 2, 3}; v[n_] := v[n]= M.v[n-1]; Table[Floor[v[n][[1]]], {n, 30}] Det[M - x*IdentityMatrix[4]] (* Second program *) a[n_]:= a[n] = If[n<5, n-1, (n-3)*a[n-1] + a[n-4]]; Table[a[n], {n, 30}] (* G. C. Greubel, Oct 05 2019 *) PROG (PARI) my(m=30, v=concat([0, 1, 2, 3], vector(m-4))); for(n=5, m, v[n]=(n-3)*v[n-1] +v[n-4]); v \\ G. C. Greubel, Oct 05 2019 (MAGMA) I:=[0, 1, 2, 3]; [n le 4 select I[n] else (n-3)*Self(n-1) + Self(n-4): n in [1..30]]; // G. C. Greubel, Oct 05 2019 (Sage) def a(n):     if (n<5): return n-1     else: return (n-3)*a(n-1) + a(n-4) [a(n) for n in (1..30)] # G. C. Greubel, Oct 05 2019 (GAP) a:= function(n)     if n<5 then return n-1;     else return (n-3)*a(n-1) + a(n-4);     fi;   end; List([1..30], n-> a(n) ); # G. C. Greubel, Oct 05 2019 CROSSREFS Sequence in context: A233239 A018290 A182250 * A075633 A141048 A326030 Adjacent sequences:  A121956 A121957 A121958 * A121960 A121961 A121962 KEYWORD nonn AUTHOR Roger L. Bagula, Sep 02 2006 EXTENSIONS Definition replaced with recurrence by the Assoc. Eds. of the OEIS, Mar 27 2010 STATUS approved

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Last modified January 28 03:20 EST 2022. Contains 350654 sequences. (Running on oeis4.)