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A011881
a(n) = floor(n*(n-1)/28).
0
0, 0, 0, 0, 0, 0, 1, 1, 2, 2, 3, 3, 4, 5, 6, 7, 8, 9, 10, 12, 13, 15, 16, 18, 19, 21, 23, 25, 27, 29, 31, 33, 35, 37, 40, 42, 45, 47, 50, 52, 55, 58, 61, 64, 67, 70, 73, 77, 80, 84, 87, 91, 94, 98, 102, 106, 110, 114, 118
OFFSET
0,9
LINKS
Index entries for linear recurrences with constant coefficients, signature (2, -1, 0, 0, 0, 0, 1, -2, 1, 0, 0, 0, 0, -1, 2, -1, 0, 0, 0, 0, 1, -2, 1).
FORMULA
G.f.: (x^6 (-1-(-1+x) x (1+(-1+x) x) (1+x^2) (1+x+x^2) (1-x^2+x^4)))/(-1+x (2+x (-1+(-1+x)^2 x^5 (1-x^7+x^14)))) Peter J. C. Moses, Jun 01 2014
a(n)= +2*a(n-1) -a(n-2) +a(n-7) -2*a(n-8) +a(n-9) -a(n-14) +2*a(n-15) -a(n-16) +a(n-21) -2*a(n-22) +a(n-23). - R. J. Mathar, Aug 11 2021
MATHEMATICA
Table[Floor[(n(n-1))/28], {n, 0, 60}] (* or *) LinearRecurrence[{2, -1, 0, 0, 0, 0, 1, -2, 1, 0, 0, 0, 0, -1, 2, -1, 0, 0, 0, 0, 1, -2, 1}, {0, 0, 0, 0, 0, 0, 1, 1, 2, 2, 3, 3, 4, 5, 6, 7, 8, 9, 10, 12, 13, 15, 16}, 60] (* Harvey P. Dale, Apr 18 2022 *)
CROSSREFS
Sequence in context: A062049 A025764 A237119 * A366853 A076678 A029024
KEYWORD
nonn,easy
AUTHOR
STATUS
approved