A392420 - OEIS

%I #8 Jan 13 2026 19:33:50

%S 11,94,678,3771,16724,61382,192280,528267,1302956,2940272,6162266,

%T 12137259,22677276,40494626,69528380,115352395,185677428,290960780,

%U 445137806,666490523,978669444,1411885662,2004291104,2803565771,3868731676,5272214088,7102171586,9465117323

%N Number of mutual-visibility sets in the n X 4 grid graph.

%H Andrew Howroyd, <a href="/A392420/b392420.txt">Table of n, a(n) for n = 1..1000</a>

%H <a href="/index/Rec#order_09">Index entries for linear recurrences with constant coefficients</a>, signature (9,-36,84,-126,126,-84,36,-9,1)

%F a(n) = (8*n^8 + 32*n^7 - 107*n^6 + 179*n^5 + 2767*n^4 + 2573*n^3 - 31108*n^2 + 46176*n + 3960)/360 for n >= 3.

%F G.f.: x*(11 - 5*x + 228*x^2 + 129*x^3 + 683*x^4 + 128*x^5 - 350*x^6 - 99*x^7 + 290*x^8 - 141*x^9 + 22*x^10)/(1 - x)^9.

%o (PARI) a(n) = if(n==1, 11, n==2, 94, (8*n^8 + 32*n^7 - 107*n^6 + 179*n^5 + 2767*n^4 + 2573*n^3 - 31108*n^2 + 46176*n + 3960)/360)

%Y Row 4 of A392417.

%K nonn,easy

%O 1,1

%A _Andrew Howroyd_, Jan 13 2026