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a(0)=0; a(n)=a(n-1)-n, if a(n-1)>2n; otherwise a(n)=a(n-1)+n.
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%I #10 Feb 28 2022 16:51:02

%S 0,1,3,6,10,15,9,16,24,15,25,14,26,39,25,40,24,41,23,42,22,43,65,42,

%T 66,41,67,40,68,39,69,38,70,37,71,36,72,109,71,110,70,111,69,112,68,

%U 113,67,114,66,115,65,116,64,117,63,118,62,119,61,120,180,119,181,118,182,117

%N a(0)=0; a(n)=a(n-1)-n, if a(n-1)>2n; otherwise a(n)=a(n-1)+n.

%H Robert Israel, <a href="/A126234/b126234.txt">Table of n, a(n) for n = 0..10000</a>

%p A[0]:= 0:

%p for n from 1 to 100 do

%p if A[n-1]>2*n then A[n]:= A[n-1]-n else A[n]:= A[n-1]+n fi

%p od:

%p seq(A[i],i=0..100); # _Robert Israel_, Nov 16 2016

%t s={0};a=0;Do[a=a+If[a>2n,-n,n];AppendTo[s,a],{n,200}];s

%t nxt[{n_,a_}]:={n+1,If[a>2(n+1),a-n-1,a+n+1]}; NestList[nxt,{0,0},70][[All,2]] (* _Harvey P. Dale_, Feb 28 2022 *)

%K nonn,look

%O 0,3

%A _Zak Seidov_, Mar 08 2007