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A011868
a(n) = floor(n*(n-1)/15).
0
0, 0, 0, 0, 0, 1, 2, 2, 3, 4, 6, 7, 8, 10, 12, 14, 16, 18, 20, 22, 25, 28, 30, 33, 36, 40, 43, 46, 50, 54, 58, 62, 66, 70, 74, 79, 84, 88, 93, 98, 104, 109, 114, 120, 126, 132, 138, 144, 150, 156, 163, 170, 176, 183, 190, 198, 205, 212, 220, 228, 236, 244, 252
OFFSET
0,7
FORMULA
From R. J. Mathar, Apr 15 2010: (Start)
a(n) = 2*a(n-1) - a(n-2) + a(n-15) - 2*a(n-16) + a(n-17).
G.f.: x^5*(1+x^2*(-1+x*(1+x^2*(1+x*(-1+x^2)))))/(1+x*(-2+x*(1+x^13*(-1+(2-x)*x)))). (End)
MATHEMATICA
LinearRecurrence[{2, -1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, -2, 1}, {0, 0, 0, 0, 0, 1, 2, 2, 3, 4, 6, 7, 8, 10, 12, 14, 16}, 63] (* Georg Fischer, Aug 15 2021 *)
CROSSREFS
Sequence in context: A144367 A370778 A075465 * A145813 A240865 A039859
KEYWORD
nonn,easy
AUTHOR
STATUS
approved