A282778 First differences of A281687.

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

Offset: 1

Author

Altug Alkan, Feb 21 2017

Keywords

• sign

Comments

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.

Links

• Altug Alkan, Table of n, a(n) for n = 1..10000
• Altug Alkan, Alternative Scatterplot of A282778

Crossrefs

Cf. A281687.

Programs

PARI

a281687(n) = sum(k=1, n, istotient(k) && istotient(2*n-k));
a(n) = a281687(n+1) - a281687(n);

Formula

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