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A140756 Count up to k sequence with alternating signs (k always positive). 1
1, -1, 2, 1, -2, 3, -1, 2, -3, 4, 1, -2, 3, -4, 5, -1, 2, -3, 4, -5, 6, 1, -2, 3, -4, 5, -6, 7, -1, 2, -3, 4, -5, 6, -7, 8, 1, -2, 3, -4, 5, -6, 7, -8, 9, -1, 2, -3, 4, -5, 6, -7, 8, -9, 10, 1, -2, 3, -4, 5, -6, 7, -8, 9, -10, 11, -1, 2, -3, 4, -5, 6, -7, 8, -9, 10, -11, 12, 1, -2, 3, -4, 5, -6, 7, -8, 9, -10, 11, -12, 13 (list; table; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

Row sums are A004526(n+1).

LINKS

Table of n, a(n) for n=1..91.

FORMULA

Regarded as a triangle, T(n,k) = (-1)^{n-k} * k.

a(n)=A002260(n)*(-1)^(A004736(n)+1); a(n)=i*(-1)^(j+1), where i=n-t*(t+1)/2, j=(t*t+3*t+4)/2-n, t=floor((-1+sqrt(8*n-7))/2). - Boris Putievskiy, Mar 14 2013

EXAMPLE

Triangle begins:

   1;

  -1,  2;

   1, -2,  3;

  -1,  2, -3,  4;

   1, -2,  3, -4,  5;

  -1,  2, -3,  4, -5,  6;

CROSSREFS

Cf. A002260, A140757, A004736.

Sequence in context: A138060 A023121 A136261 * A002260 A243732 A194905

Adjacent sequences:  A140753 A140754 A140755 * A140757 A140758 A140759

KEYWORD

easy,sign,tabl

AUTHOR

Franklin T. Adams-Watters, May 27 2008

STATUS

approved

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Last modified June 28 08:51 EDT 2022. Contains 354903 sequences. (Running on oeis4.)