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A154990 Triangle read by rows. Main diagonal is positive. The rest of the terms are negative. 7
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)
OFFSET

1,1

COMMENTS

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

LINKS

Table of n, a(n) for n=1..73.

EXAMPLE

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;

MAPLE

(Excel cell formula) =if(row()>=column(); if(row()>=column(); 1; "")*if(row()>column(); -1; 1); "")

MATHEMATICA

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 *)

CROSSREFS

Sequence in context: A160357 A057077 A070748 * A209615 A156734 A119664

Adjacent sequences:  A154987 A154988 A154989 * A154991 A154992 A154993

KEYWORD

sign,easy,tabl

AUTHOR

Mats Granvik, Jan 18 2009

STATUS

approved

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Last modified August 27 20:22 EDT 2014. Contains 246147 sequences.