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A101884 Smallest increasing natural number sequence without any length 3 equidistant arithmetic subsequences. 7
1, 2, 4, 5, 8, 9, 11, 12, 16, 18, 19, 21, 26, 28, 29, 32, 33, 35, 36, 39, 43, 44, 46, 47, 54, 56, 59, 60, 62, 63, 68, 69, 71, 72, 80, 82, 86, 88, 91, 93, 94, 99, 103, 106, 113, 115, 116, 120, 122, 127, 130, 131, 133, 134, 137, 141, 142, 144, 145, 149, 154 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

If the restriction "increasing" is removed sequence A094870 is obtained.

LINKS

Nathaniel Johnston, Table of n, a(n) for n = 1..5000

Index entries related to non-averaging sequences

EXAMPLE

3 is out because of 1,2,3. 7 is out because of 1,4,7.

8 is allowed even though 2,5,8 appears in the sequence, because 2, 5, and 8 are not spaced equidistant within the sequence.

MAPLE

lim:=61: a[1]:=1:a[2]:=2: for n from 3 to lim do na := {}: for j from 1 to floor((n-1)/2) do na := na union {2*a[n-j]-a[n-2*j]}: od: for j from a[n-1]+1 do if(not member(j, na))then a[n]:=j:break: fi: od:od: seq(a[n], n=1..lim); # Nathaniel Johnston, Jun 16 2011

CROSSREFS

Cf. A101885, A101886, A101888. Also A094870.

Sequence in context: A288214 A117121 A101925 * A118179 A096603 A084464

Adjacent sequences:  A101881 A101882 A101883 * A101885 A101886 A101887

KEYWORD

nonn,easy

AUTHOR

Douglas Stones (dssto1(AT)student.monash.edu.au), Dec 20 2004

STATUS

approved

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Last modified February 20 09:06 EST 2018. Contains 299384 sequences. (Running on oeis4.)