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%I #16 Apr 25 2018 11:49:56
%S 4,10,25,70,238,901,3445,13390,52942,210226,838450,3350725,13393093,
%T 53547790,214151950,856558645,3426077749,13703917774,54815043790,
%U 219258602290,877031899954,3508124454085,14032487779525,56129938535185,224519713993489,898078755310654
%N Number of squares in triangle-shaped polyominoes obtained by adding three identical polyominoes to the previous one, starting with one L-tetromino.
%C Each polyomino a(n) has a width of A282390(n+1) squares and a height of A000051(n) squares.
%H Daniel Poveda Parrilla, <a href="/A282389/a282389.gif">Illustration of initial terms</a>
%F a(0) = 4; a(n) = a(n-1) + 3*(A282390(n)*A000051(n-1) - a(n-1)) for n > 0.
%F a(n) = A282390(n+(n mod 2))*A000051(n-(n mod 2)) for n > 0.
%F a(n) = (A282390(n+(n mod 2)) - A000051(n-1+(n mod 2)))*A000051(n-(n mod 2)) + A028401(n+2) for n > 0.
%o (Python)
%o m = [3, 1]
%o for i in range(25):
%o w, h = m[0], len(m)
%o print(sum(m)) # print(w) for widths of the polyominoes
%o m2 = [w-x for x in reversed(m) if w>x]
%o m = [w+x for x in m2] + [w for x in m if x==w] + m2
%o # _Andrey Zabolotskiy_, Feb 14 2017
%Y Cf. A000051, A028401, A282390.
%K nonn
%O 0,1
%A _Daniel Poveda Parrilla_, Feb 14 2017
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