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%I #42 Jul 09 2021 12:18:22
%S 1,3,6,2,7,1,8,16,7,17,6,18,5,19,4,20,3,21,2,22,1,23,46,22,47,21,48,
%T 20,49,19,50,18,51,17,52,16,53,15,54,14,55,13,56,12,57,11,58,10,59,9,
%U 60,8,61,7,62,6,63,5,64,4,65,3,66,2,67,1,68,136,67,137
%N a(n) = a(n-1) - n if a(n-1) > n, else a(n) = a(n-1) + n.
%C Variation (1) on Recamán's sequence A005132.
%C a(A134931(n-1)) = 1. - _Reinhard Zumkeller_, Jan 31 2013
%H N. J. A. Sloane, <a href="/A046901/b046901.txt">First 10000 terms</a>
%H Nick Hobson, <a href="/A046901/a046901.py.txt">Python program for this sequence</a>
%H Kival Ngaokrajang, <a href="/A046901/a046901.pdf">scatter plot in log-log scale looks</a>, for both this sequence and A211346.
%H <a href="/index/Rea#Recaman">Index entries for sequences related to Recamán's sequence</a>
%F This is a concatenation S_0, S_1, S_2, ... where S_i = [b_0, b_1, ..., b_{k-1}], k=5*3^i, with b_0 = 1, b_{2j} = k+j, b_{2j+1} = (k+1)/2-j. E.g., S_0 = [1, 3, 6, 2, 7].
%F For any m>=1, for k such that 5*3^k+3>12m, a((5*3^k+3-12*m)/6)= m. For example, for k>=1, a((5*3^k-9)/6) = 1. - _Benoit Cloitre_, Oct 31 2002
%F a(n) = A008343(n+1) + 1. - _Jon Maiga_, Jul 09 2021
%p A046901 := proc(n) option remember; if n = 1 then 1 else if A046901(n-1)>n then A046901(n-1)-n else A046901(n-1)+n; fi; fi; end;
%t a[1]=1;a[n_]:=a[n]=If[a[n-1]>n,a[n-1]-n,a[n-1]+n]; Table[a[i],{i,70}] (* _Harvey P. Dale_, Apr 01 2011 *)
%t nxt[{n_,a_}]:={n+1,If[a>n+1,a-n-1,a+n+1]}; NestList[nxt,{1,1},70][[All,2]] (* _Harvey P. Dale_, Jun 01 2019 *)
%o (PARI) a(n)=if(n<2,1,a(n-1)-if(sign(n-a(n-1))+1,-1,1)*n);
%o (Haskell)
%o a046901 n = a046901_list !! (n-1)
%o a046901_list = scanl1 (\u v -> if u > v then u - v else u + v) [1..]
%o -- _Reinhard Zumkeller_, Dec 07 2015, Jan 31 2013
%Y Cf. A008343, A008344, A005132.
%Y Cf. A076039, A003462, A076041, A076042, A057198.
%Y Cf. A085059.
%Y Cf. A238324.
%K easy,nonn,nice,look
%O 1,2
%A _N. J. A. Sloane_
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