A209386 - OEIS

%I #13 Jan 04 2018 01:33:56

%S 0,2,6,12,4,14,26,40,24,42,22,44,20,46,18,48,16,50,86,124,84,126,82,

%T 36,84,34,86,32,88,30,90,28,92,158,226,156,228,154,78,156,76,158,74,

%U 160,72,162,70,164,68,166,66,168,64,170,62,172,60,174,58,176,56,178,54,180,52,182,314,448,312,450,310

%N a(n) = 2*A005132(n).

%C This is the even-numbers version of Recamán's sequence A005132: a(0)=0; for n>0, a(n) = a(n-1)-2n if that number is >= 0 and not already in the sequence, otherwise a(n) = a(n-1)+2n.

%H G. C. Greubel, <a href="/A209386/b209386.txt">Table of n, a(n) for n = 0..1000</a>

%t f[s_List]:= Block[{a = s[[-1]], len = Length@s}, Append[s, If[a > len && ! MemberQ[s, a - len], a - len, a + len]]]; A005132:= Nest[f, {0}, 130]; Table[2*A005132[[n]], {n, 1, 50}] (* _G. C. Greubel_, Jan 03 2018 *)

%Y Cf. A005132, A209387.

%K nonn

%O 0,2

%A _N. J. A. Sloane_, Mar 07 2012