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A117713 a(1)=1, a(2)=3, a(3)=8; for n>=4, a(n) = 10*a(n-3) + 8 (if a(n-3) is odd) or + 9 if a(n-3) is even). 0

%I

%S 1,3,8,18,38,89,189,389,898,1898,3898,8989,18989,38989,89898,189898,

%T 389898,898989,1898989,3898989,8989898,18989898,38989898,89898989,

%U 189898989,389898989,898989898,1898989898,3898989898,8989898989,18989898989,38989898989,89898989898

%N a(1)=1, a(2)=3, a(3)=8; for n>=4, a(n) = 10*a(n-3) + 8 (if a(n-3) is odd) or + 9 if a(n-3) is even).

%C From a puzzle (1,3,8,18,?,89,189) given on a civil service test.

%p f:=proc(n) option remember; local t1; if n=1 then RETURN(1); fi; if n=2 then RETURN(3); fi; if n=3 then RETURN(8); fi; t1:=10*f(n-3)+8; if f(n-3) mod 2 = 0 then t1:=t1+1; fi; RETURN(t1); end;

%K nonn

%O 1,2

%A Louis Ciotti (lciotti(AT)twcny.rr.com), Apr 13 2006

%E Solution proposed by Mohammed BOUAYOUN (mohammed.bouayoun(AT)yahoo.fr), Apr 14 2006

%E Another possibility is that 1,3,8,18,?,89,189,... is an erroneous version of A117727. - _Hugo van der Sanden_, Apr 14 2006

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Last modified January 29 07:19 EST 2023. Contains 359915 sequences. (Running on oeis4.)