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A262942 Sequence of positive integers where each is chosen to be as small as possible subject to the conditions that no three terms a(j), a(j+k), a(j+2k) (for any j and k) form an arithmetic progression (in any order) and that no term repeats. 2
1, 2, 4, 5, 8, 3, 7, 6, 10, 11, 14, 9, 16, 12, 13, 19, 15, 18, 20, 21, 26, 17, 22, 24, 25, 27, 31, 28, 23, 32, 29, 34, 37, 38, 40, 41, 35, 30, 42, 46, 47, 54, 36, 33, 45, 43, 49, 39, 48, 50, 55, 52, 53, 44, 59, 57, 51, 60, 56, 61, 62, 67, 58, 69, 64, 72, 66, 68, 76, 71, 73, 77, 65, 75, 63, 88, 89, 80, 78, 74, 83, 79, 70, 90, 94, 82, 81, 84, 85, 91, 87, 101 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Conjectured permutation of the natural numbers.

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

EXAMPLE

For n = 4, 3 is not available because (a(2)=2, 3, a(3)=4} form an arithmetic progression, 1,2,4 are already used, so a(4) = 5. - Robert Israel, Nov 15 2015

MAPLE

N:= 1000: # to get all terms before the first > N

V:= Vector(N):

S:= Vector(N):

firstav:= 1;

for n from 1 to N do

    forbid:= {seq(op([2*V[k]-V[2*k-n], 2*V[2*k-n]-V[k], (V[k]+V[2*k-n])/2]), k=ceil((n+1)/2)..n-1)};

    for v from firstav to N do

      if S[v] <> 0 and v = firstav then firstav:= v+1 fi;

      if S[v] = 0 and not member(v, forbid) then

        V[n]:= v;

        S[v]:= 1;

        break

      fi

    od;

    if v > N then break fi;

od:

seq(V[i], i=1..n-1); # Robert Israel, Nov 15 2015

CROSSREFS

A229037 has a very similar definition, but a totally different graph.

Sequence in context: A324331 A101410 A110991 * A076990 A330434 A330424

Adjacent sequences:  A262939 A262940 A262941 * A262943 A262944 A262945

KEYWORD

nonn

AUTHOR

Max Barrentine, Oct 05 2015

EXTENSIONS

Added more terms from b-file. - N. J. A. Sloane, Nov 26 2015

STATUS

approved

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Last modified February 25 11:07 EST 2020. Contains 332231 sequences. (Running on oeis4.)