cp's OEIS Frontend

A127949 A000012 as an infinite lower triangular matrix with all 1's; A127899 = a simple transform; then A000012 * A127899. Given A051340, change all 1's to -1. Triangle read by rows, (n-1) -1's followed by "n".

%I A127949 #8 Aug 18 2015 00:06:48
%S A127949 1,-1,2,-1,-1,3,-1,-1,-1,4,-1,-1,-1,-1,5,-1,-1,-1,-1,-1,6,-1,-1,-1,-1,
%T A127949 -1,-1,7,-1,-1,-1,-1,-1,-1,-1,8,-1,-1,-1,-1,-1,-1,-1,-1,9,-1,-1,-1,-1,
%U A127949 -1,-1,-1,-1,-1,10,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,11,-1,-1,-1,-1,-1,-1
%N A127949 A000012 as an infinite lower triangular matrix with all 1's; A127899 = a simple transform; then A000012 * A127899. Given A051340, change all 1's to -1. Triangle read by rows, (n-1) -1's followed by "n".
%C A127949 For the inverse of A127949 see A126615, a harmonic triangle.
%C A127949 This is one way to define an inverse to A000217. - _R. J. Mathar_, Apr 30 2010
%e A127949 First few rows of the triangle are:
%e A127949 1;
%e A127949 -1, 2;
%e A127949 -1, -1, 3;
%e A127949 -1, -1, -1, 4;
%e A127949 ...
%p A127949 A127949 := proc(n) if issqr(1+8*n) then (sqrt(1+8*n)-1)/2 ; else -1 ; end if; end proc: seq(A127949(n),n=1..120) ; # _R. J. Mathar_, Apr 30 2010
%Y A127949 Cf. A000012, A127899, A051340, A126615.
%K A127949 tabl,sign,easy
%O A127949 1,3
%A A127949 _Gary W. Adamson_, Feb 09 2007
%E A127949 More terms from _R. J. Mathar_, Apr 30 2010