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A255325
Half of the difference between the n-th Ludic number and the n-th noncomposite: a(n) = (A003309(n) - A008578(n))/2.
2
0, 0, 0, 0, 0, 0, 0, 0, 2, 1, 0, 3, 2, 1, 2, 3, 4, 4, 5, 5, 6, 8, 6, 7, 9, 9, 9, 9, 10, 11, 15, 11, 13, 12, 17, 13, 14, 12, 15, 21, 19, 21, 21, 18, 20, 19, 20, 18, 17, 19, 24, 25, 24, 30, 28, 28, 33, 31, 33, 32, 36, 38, 34, 35, 36, 38, 40, 38, 39, 36, 36, 39, 37, 35, 36, 42, 42, 43, 42, 46, 44, 42, 44, 43, 47, 48, 49, 52
OFFSET
1,9
LINKS
FORMULA
a(n) = A255324(n)/2 = (A003309(n) - A008578(n))/2.
MATHEMATICA
t = Range[2, 1000];
A003309 = {1};
While[Length[t] > 0, k = First[t];
AppendTo[A003309, k]; t = Drop[t, {1, -1, k}]];
a[n_] := If[n == 1, 0, A003309[[n]] - Prime[n - 1]]/2;
Array[a, Length[A003309]] (* Jean-François Alcover, Jan 08 2022, after Ray Chandler in A003309 *)
PROG
(Scheme) (define (A255325 n) (/ (A255324 n) 2))
CROSSREFS
Cf. A255324 (the same terms multipled by 2).
Sequence in context: A274183 A212278 A244215 * A025654 A025648 A025655
KEYWORD
nonn
AUTHOR
Antti Karttunen, Feb 23 2015
STATUS
approved