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A154990
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Triangle read by rows. Main diagonal is positive. The rest of the terms are negative.
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8
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1, -1, 1, -1, -1, 1, -1, -1, -1, 1, -1, -1, -1, -1, 1, -1, -1, -1, -1, -1, 1, -1, -1, -1, -1, -1, -1, 1, -1, -1, -1, -1, -1, -1, -1, 1, -1, -1, -1, -1, -1, -1, -1, -1, 1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 1, -1, -1, -1, -1, -1, -1, -1
(list;
table;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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1,1
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COMMENTS
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Triangle can be used in matrix inverses. Signs in columns as in A153881.
Iff n is a triangular number, a(n)=1; otherwise, a(n)=-1. (This is explicitly implemented in the second Mathematica program below.) - Harvey P. Dale, Apr 27 2014
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LINKS
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Table of n, a(n) for n=1..73.
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EXAMPLE
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Table begins:
1;
-1,1;
-1,-1,1;
-1,-1,-1,1;
-1,-1,-1,-1,1;
-1,-1,-1,-1,-1,1;
-1,-1,-1,-1,-1,-1,1;
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MAPLE
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A154990 := proc(n, k)
option remember;
if k = n then
1;
elif k > n then
0;
else
-1 ;
end if;
end proc:
seq(seq(A154990(n, k), k=1..n), n=1..12) ; # R. J. Mathar, Sep 16 2017
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MATHEMATICA
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Flatten[Table[PadLeft[{1}, n, -1], {n, 15}]] (* or *) With[{tr=Accumulate[ Range[ 15]]}, Table[If[MemberQ[tr, n], 1, -1], {n, Last[tr]}]] (* Harvey P. Dale, Apr 27 2014 *)
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PROG
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(Excel) =if(row()>=column(); if(row()>=column(); 1; "")*if(row()>column(); -1; 1); "")
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CROSSREFS
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Sequence in context: A057077 A262725 A070748 * A209615 A242179 A319117
Adjacent sequences: A154987 A154988 A154989 * A154991 A154992 A154993
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KEYWORD
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sign,easy,tabl
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AUTHOR
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Mats Granvik, Jan 18 2009
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STATUS
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approved
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