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First trisection of A028560.
1

%I #16 Apr 10 2018 13:38:16

%S 0,27,72,135,216,315,432,567,720,891,1080,1287,1512,1755,2016,2295,

%T 2592,2907,3240,3591,3960,4347,4752,5175,5616,6075,6552,7047,7560,

%U 8091,8640,9207,9792,10395,11016

%N First trisection of A028560.

%C Nonnegative k such that k/9 + 1 is a square. - _Bruno Berselli_, Apr 10 2018

%H <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (3,-3,1).

%F a(n) = 9*n*(n+2).

%F a(n) = a(n-1) + 9*A144396(n) for n>0.

%t Table[9 n (n + 2), {n, 0, 40}] (* _Harvey P. Dale_, Feb 20 2011 *)

%o (PARI) a(n)=9*n*(n+2) \\ _Charles R Greathouse IV_, Jun 17 2017

%Y Cf. A144396, A144454.

%K nonn,easy

%O 0,2

%A _Paul Curtz_, Nov 09 2008

%E More terms from _Vincenzo Librandi_, Nov 26 2010