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A209386 a(n) = 2*A005132(n). 2
0, 2, 6, 12, 4, 14, 26, 40, 24, 42, 22, 44, 20, 46, 18, 48, 16, 50, 86, 124, 84, 126, 82, 36, 84, 34, 86, 32, 88, 30, 90, 28, 92, 158, 226, 156, 228, 154, 78, 156, 76, 158, 74, 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 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

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.

LINKS

G. C. Greubel, Table of n, a(n) for n = 0..1000

MATHEMATICA

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 *)

CROSSREFS

Cf. A005132, A209387.

Sequence in context: A188894 A054579 A277962 * A205103 A165822 A014965

Adjacent sequences:  A209383 A209384 A209385 * A209387 A209388 A209389

KEYWORD

nonn

AUTHOR

N. J. A. Sloane, Mar 07 2012

STATUS

approved

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Last modified December 13 22:55 EST 2019. Contains 329974 sequences. (Running on oeis4.)