The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 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 G. C. Greubel, Rows n = 1..30 of the triangle, flattened FORMULA From G. C. Greubel, Mar 06 2021: (Start) T(n, k) = -1 with T(n, n) = 1. Sum_{k=1..n} T(n, k) = 2-n = -A023443(n-1) = -A023444(n). (End) 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 (Sage) flatten([[1 if k==n else -1 for k in (1..n)] for n in (1..12)]) # G. C. Greubel, Mar 06 2021 (Magma) [k eq n select 1 else -1: k in [1..n], n in [1..12]]; // G. C. Greubel, Mar 06 2021 CROSSREFS Cf. A023443, A023444. 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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified February 2 06:25 EST 2023. Contains 360000 sequences. (Running on oeis4.)