|
|
A282778
|
|
First differences of A281687.
|
|
2
|
|
|
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
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,23
|
|
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
|
|
|
FORMULA
|
|
|
PROG
|
(PARI) a281687(n) = sum(k=1, n, istotient(k) && istotient(2*n-k));
a(n) = a281687(n+1) - a281687(n);
|
|
CROSSREFS
|
|
|
KEYWORD
|
sign
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|