cp's OEIS Frontend

A211906 Number of lower triangular n X n arrays colored with integers 0 upwards introduced in row major order, with no element equal to any horizontal or vertical neighbor, and containing the value n(n+1)/2-3.

%I A211906 #6 Jun 02 2025 07:51:18
%S A211906 0,2,30,418,3006,14201,51157,152650,396538,926011,1987151,3980637,
%T A211906 7530745,13575108,23479016,39178351,63355567,99653440,152931628,
%U A211906 229571396,337834176,488279947,694251735
%N A211906 Number of lower triangular n X n arrays colored with integers 0 upwards introduced in row major order, with no element equal to any horizontal or vertical neighbor, and containing the value n(n+1)/2-3.
%C A211906 Column 2 of A211910
%F A211906 Empirical: a(n) = (1/128)*n^8 + (1/32)*n^7 - (29/192)*n^6 - (5/16)*n^5 + (193/128)*n^4 - (25/96)*n^3 - (275/96)*n^2 + (49/24)*n + 1 for n>1
%e A211906 Some solutions for n=4
%e A211906 ..0........0........0........0........0........0........0........0
%e A211906 ..1.2......1.2......1.2......1.2......1.2......1.2......1.2......1.2
%e A211906 ..3.4.5....3.4.5....3.4.5....3.4.2....3.4.5....3.4.5....2.3.4....3.4.5
%e A211906 ..6.7.0.8..6.0.1.7..6.3.7.8..5.6.7.3..1.5.6.7..6.2.7.5..5.6.0.7..6.2.6.7
%K A211906 nonn
%O A211906 1,2
%A A211906 _R. H. Hardin_ Apr 25 2012