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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

Altug Alkan, Table of n, a(n) for n = 1..10000

Altug Alkan, Alternative Scatterplot of A282778

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: A025924 A025904 A137993 * A059883 A086967 A098490

Adjacent sequences:  A282775 A282776 A282777 * A282779 A282780 A282781

KEYWORD

sign

AUTHOR

Altug Alkan, Feb 21 2017

STATUS

approved

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Last modified October 20 14:22 EDT 2018. Contains 316381 sequences. (Running on oeis4.)