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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
a(n) = A281687(n+1) - A281687(n).
PROG
(PARI) a281687(n) = sum(k=1, n, istotient(k) && istotient(2*n-k));
a(n) = a281687(n+1) - a281687(n);
CROSSREFS
Cf. A281687.
Sequence in context: A025904 A137993 A353329 * A342788 A059883 A086967
KEYWORD
sign
AUTHOR
Altug Alkan, Feb 21 2017
STATUS
approved

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Last modified April 16 20:42 EDT 2024. Contains 371754 sequences. (Running on oeis4.)