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%I #23 Feb 26 2024 01:55:27
%S 1,11,6,16,11,21,16,26,21,31,26,36,31,41,36,46,41,51,46,56,51,61,56,
%T 66,61,71,66,76,71,81,76,86,81,91,86,96,91,101,96,106,101,111,106,116,
%U 111,121,116,126,121,131,126,136,131,141,136,146,141,151,146,156,151,161,156,166,161,171
%N Add 10, subtract 5, add 10, subtract 5, ad infinitum.
%C A brain teaser.
%H <a href="http://mathcentral.uregina.ca/QQ/database/QQ.09.03/megan1.html">Math. Central U. Regina, no. 377 of QQ03</a>
%H <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (1,1,-1).
%F a(2j+1) = 5j+1, a(2j) = 5j+6. - _Robert G. Wilson v_, Nov 26 2006; _R. J. Mathar_, Jul 09 2009
%F From _R. J. Mathar_, Jul 09 2009: (Start)
%F G.f.: x*(1+10*x-6*x^2)/((1+x)*(1-x)^2).
%F a(n) = 9/4+5*n/2+15*(-1)^n/4. (End)
%F a(n) = a(n-1)+a(n-2)-a(n-3). - _Wesley Ivan Hurt_, Mar 14 2015
%p A122088:=n->9/4 + 5*n/2 + 15*(-1)^n/4: seq(A122088(n), n=1..50); # _Wesley Ivan Hurt_, Mar 14 2015
%t Table[9/4 + 5*n/2 + 15*(-1)^n/4, {n, 50}] (* _Wesley Ivan Hurt_, Mar 14 2015 *)
%t LinearRecurrence[{1,1,-1},{1,11,6},70] (* _Harvey P. Dale_, Dec 06 2017 *)
%o (Magma) [9/4 + 5*n/2 + 15*(-1)^n/4 : n in [1..50]]; // _Wesley Ivan Hurt_, Mar 14 2015
%K nonn,easy
%O 1,2
%A Chris H. (chrishale(AT)deotte.com), Oct 17 2006
%E Present definition supplied by _R. J. Mathar_, Oct 20 2006
%E More terms from _Robert G. Wilson v_, Nov 26 2006
%E Formulas adapted to offset by _R. J. Mathar_, Jul 09 2009
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