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 A154990 Triangle read by rows. Main diagonal is positive. The rest of the terms are negative. 8
 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 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 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 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 *) PROG (Excel) =if(row()>=column(); if(row()>=column(); 1; "")*if(row()>column(); -1; 1); "") CROSSREFS Sequence in context: A057077 A262725 A070748 * A209615 A242179 A319117 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 January 21 13:17 EST 2019. Contains 319350 sequences. (Running on oeis4.)