cp's OEIS Frontend

A252821 Number of n X n nonnegative integer arrays with upper left 0 and every value within 3 of its city block distance from the upper left and every value increasing by 0 or 1 with every step right or down.

%I A252821 #8 Jul 23 2025 13:40:24
%S A252821 1,6,81,1920,54376,1679072,55960651,2001017650,76084625352,
%T A252821 3047083917080,127445868976818,5528160760257164,247294135503496534,
%U A252821 11357522219262644466,533619846702969331737,25573797311727396663076
%N A252821 Number of n X n nonnegative integer arrays with upper left 0 and every value within 3 of its city block distance from the upper left and every value increasing by 0 or 1 with every step right or down.
%C A252821 Diagonal of A252828
%H A252821 R. H. Hardin, <a href="/A252821/b252821.txt">Table of n, a(n) for n = 1..25</a>
%e A252821 Some solutions for n=4
%e A252821 ..0..1..2..3....0..1..1..2....0..1..1..2....0..1..2..3....0..1..2..2
%e A252821 ..0..1..2..3....0..1..2..3....0..1..1..2....1..2..3..4....0..1..2..2
%e A252821 ..1..2..3..4....1..2..3..3....0..1..2..3....2..3..3..4....1..2..3..3
%e A252821 ..2..3..4..5....2..2..3..4....1..2..2..3....3..4..4..5....2..3..3..3
%K A252821 nonn
%O A252821 1,2
%A A252821 _R. H. Hardin_, Dec 22 2014