This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A185515 #13 Apr 16 2018 08:59:17 %S A185515 593,12361,154561,2490449,35659489,541370505,7998109489,119752453041, %T A185515 1781802607473,26592505725449,396308610878561,5910310463665361, %U A185515 88113720913502145,1313850510428863561,19589143573382779985 %N A185515 Number of (n+1) X 4 0..2 arrays with every 2 X 2 subblock singular. %C A185515 Column 3 of A185521. %H A185515 R. H. Hardin, <a href="/A185515/b185515.txt">Table of n, a(n) for n = 1..200</a> %F A185515 Empirical: a(n) = 21*a(n-1) - 47*a(n-2) - 1009*a(n-3) + 5624*a(n-4) - 3060*a(n-5) - 27360*a(n-6) + 36864*a(n-7). %F A185515 Empirical g.f.: x*(593 - 92*x - 77149*x^2 + 423972*x^3 - 238356*x^4 - 2179296*x^5 + 2985984*x^6) / (1 - 21*x + 47*x^2 + 1009*x^3 - 5624*x^4 + 3060*x^5 + 27360*x^6 - 36864*x^7). - _Colin Barker_, Apr 16 2018 %e A185515 Some solutions for 3 X 4: %e A185515 ..1..1..1..2....1..2..1..2....1..2..2..2....2..0..2..1....2..0..0..1 %e A185515 ..0..0..0..0....0..0..0..0....0..0..0..0....2..0..0..0....2..0..0..1 %e A185515 ..0..1..0..0....1..2..0..2....1..0..1..0....2..0..2..2....2..0..0..2 %Y A185515 Cf. A185521. %K A185515 nonn %O A185515 1,1 %A A185515 _R. H. Hardin_, Jan 29 2011