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a(n) = ceiling(n^2/11).
2

%I #21 Aug 29 2021 16:34:40

%S 0,1,1,1,2,3,4,5,6,8,10,11,14,16,18,21,24,27,30,33,37,41,44,49,53,57,

%T 62,67,72,77,82,88,94,99,106,112,118,125,132,139,146,153,161,169,176,

%U 185,193,201,210,219,228,237,246,256,266,275,286,296

%N a(n) = ceiling(n^2/11).

%H Colin Barker, <a href="/A036409/b036409.txt">Table of n, a(n) for n = 0..1000</a>

%H <a href="/index/Rec#order_13">Index entries for linear recurrences with constant coefficients</a>, signature (2,-1,0,0,0,0,0,0,0,0,1,-2,1).

%F a(n) = +2 a(n-1) -a(n-2) +a(n-11) -2 a(n-12) +a(n-13). - _R. J. Mathar_, Mar 11 2012

%F G.f.: x*(1+x)*(1-x+x^2)*(1-x+x^2-x^3+x^4)*(1-x^2+x^4) / ((1-x)^3*(1+x+x^2+x^3+x^4+x^5+x^6+x^7+x^8+x^9+x^10)). - _Colin Barker_, Apr 06 2016

%F a(m + 11 k) = a(m) + 11 k^2 + 2 m k. - _Robert Israel_, Apr 06 2016

%p seq(ceil(n^2/11),n=0..100); # _Robert Israel_, Apr 06 2016

%t Table[Ceiling[n^2/11], {n, 0, 57}] (* _Michael De Vlieger_, Apr 06 2016 *)

%t LinearRecurrence[{2,-1,0,0,0,0,0,0,0,0,1,-2,1},{0,1,1,1,2,3,4,5,6,8,10,11,14},60] (* _Harvey P. Dale_, Aug 29 2021 *)

%o (PARI) concat(0, Vec(x*(1+x)*(1-x+x^2)*(1-x+x^2-x^3+x^4)*(1-x^2+x^4) / ((1-x)^3*(1+x+x^2+x^3+x^4+x^5+x^6+x^7+x^8+x^9+x^10)) + O(x^50))) \\ _Colin Barker_, Apr 06 2016

%Y Cf. A036404, A036405, A036406, A036407, A036408.

%K nonn,easy

%O 0,5

%A _N. J. A. Sloane_