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%I #13 Feb 12 2024 12:34:43
%S 0,1,2,3,4,5,6,7,8,9,0,1,3,7,5,1,4,9,9,8,7,2,5,6,3,0,1,5,1,6,9,7,9,6,
%T 5,6,1,7,6,7,3,3,6,3,9,5,1,8,5,6,9,4,3,2,7,0,1,9,3,5,1,0,1,1,2,9,2,1,
%U 3,8,3,1,4,7,7,4,1,5,6,5,1,6,1,7,1,8,1,9,1,0,1,1,2,3,4,5,6,7,8,9,0,1,3,7,5,1,4,9,9,8,7,2,5,6,3,0,1,5,1,6
%N Dorey's period-90 sequence (periodic from a(1)=1 onward).
%H Ray Chandler, <a href="/A080867/b080867.txt">Table of n, a(n) for n = 0..1000</a>
%H <a href="/index/Rec#order_90">Index entries for linear recurrences with constant coefficients</a>, signature (0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1).
%F a(n<12) = n mod 10, a(n>11) = a(n-1)+a(i+1) mod 10, where i (< n-1) is the first position to left of n-1 where a(n-1) occurs.
%p A080867 := proc(n) option remember; local i,u; if(n < 12) then RETURN(n mod 10); else u := A080867(n-1); for i from n-2 by -1 to 0 do if(A080867(i) = u) then RETURN((A080867(i+1)+u) mod 10); fi; od; fi; RETURN(-1); end;
%Y Cf. A080868.
%K nonn,base,easy
%O 0,3
%A Laurent Dorey (laurentdorey(AT)wanadoo.fr) and _Antti Karttunen_, Feb 21 2003
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