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%I #20 Sep 08 2022 08:44:41
%S 36,169,400,729,1156,1681,2304,3025,3844,4761,5776,6889,8100,9409,
%T 10816,12321,13924,15625,17424,19321,21316,23409,25600,27889,30276,
%U 32761,35344,38025,40804,43681,46656
%N a(n) = (7*n + 6)^2.
%C If Y is a fixed 2-subset of a (7n+1)-set X then a(n-1) is the number of 3-subsets of X intersecting Y. - _Milan Janjic_, Oct 21 2007
%H Vincenzo Librandi, <a href="/A017054/b017054.txt">Table of n, a(n) for n = 0..10000</a>
%H Milan Janjic, <a href="http://www.pmfbl.org/janjic/">Two Enumerative Functions</a>
%H <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (3,-3,1).
%F a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3); a(0)=36, a(1)=169, a(2)=400. - _Harvey P. Dale_, Apr 28 2016
%t (7*Range[0,30]+6)^2 (* or *) LinearRecurrence[{3,-3,1},{36,169,400},40] (* _Harvey P. Dale_, Apr 28 2016 *)
%o (Magma) [(7*n+6)^2: n in [0..40]]; // _Vincenzo Librandi_, Jul 10 2011
%o (PARI) a(n)=(7*n+6)^2 \\ _Charles R Greathouse IV_, Jun 17 2017
%Y Cf. A017053 (7*n+6).
%K nonn,easy
%O 0,1
%A _N. J. A. Sloane_
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