A141620 - OEIS

%I #10 May 31 2017 14:42:06

%S 5,-3,10,-3,-5,17,-3,-5,-7,26,-3,-5,-7,-9,37,-3,-5,-7,-9,-11,50,-3,-5,

%T -7,-9,-11,-13,65,-3,-5,-7,-9,-11,-13,-15,82,-3,-5,-7,-9,-11,-13,-15,

%U -17,101,-3,-5,-7,-9,-11,-13,-15,-17,-19,122,-3,-5,-7,-9,-11,-13,-15,-17,-19,-21

%N First differences of A120070.

%F a(n) = mix (from 2) n^2+1 (or A002522(n+2)), (ever from -3) successive -A005408.

%F a(n) = ((A^2+3*A-2*n)*(-A^2+A+2*(n+4))-(B^2+3*B-2*(n-1))*(-B^2+B+2*(n+3)))/4, where A = floor((sqrt(8*n+9)-1)/2) and B = floor((sqrt(8*(n-1)+9)-1)/2) = floor((sqrt(8*n+1)-1)/2). - _Luce ETIENNE_, May 31 2017

%Y Cf. A120070.

%K sign

%O 0,1

%A _Paul Curtz_, Aug 23 2008