A209386 a(n) = 2*A005132(n).

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

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: A355416 A054579 A277962 * A205103 A367575 A165822

Adjacent sequences: A209383 A209384 A209385 * A209387 A209388 A209389

Keyword

nonn

Author

N. J. A. Sloane, Mar 07 2012

Status

approved