A282778 - OEIS

%I #16 Feb 28 2017 16:12:36

%S 0,0,1,0,1,0,0,0,1,0,1,0,0,0,1,0,0,0,1,-1,1,0,2,-1,1,-1,1,0,2,-1,2,-2,

%T 1,-1,2,-1,2,-3,1,1,1,-1,3,-2,-1,1,0,-1,3,-1,0,0,2,-1,4,-3,0,0,1,-2,4,

%U -4,3,-2,3,-3,4,-2,1,-1,2,-3,5,-3,2,-3,3,-2,3,-2,0,1

%N First differences of A281687.

%C Numbers n such that a(n) = 0 are 1, 2, 4, 6, 7, 8, 10, 12, 13, 14, 16, 17, 18, 22, 28, 47, 51, 52, 57, 58, 81, 111, 112, 195, 201 according to the b-file. Can there be other values of n such that a(n) = 0? See also graph of this sequence.

%H Altug Alkan, <a href="/A282778/b282778.txt">Table of n, a(n) for n = 1..10000</a>

%H Altug Alkan, <a href="/A282778/a282778.png">Alternative Scatterplot of A282778</a>

%F a(n) = A281687(n+1) - A281687(n).

%o (PARI) a281687(n) = sum(k=1, n, istotient(k) && istotient(2*n-k));

%o a(n) = a281687(n+1) - a281687(n);

%Y Cf. A281687.

%K sign

%O 1,23

%A _Altug Alkan_, Feb 21 2017