A392420 Number of mutual-visibility sets in the n X 4 grid graph.

11, 94, 678, 3771, 16724, 61382, 192280, 528267, 1302956, 2940272, 6162266, 12137259, 22677276, 40494626, 69528380, 115352395, 185677428, 290960780, 445137806, 666490523, 978669444, 1411885662, 2004291104, 2803565771, 3868731676, 5272214088, 7102171586, 9465117323

Offset

1,1

Links

Andrew Howroyd, Table of n, a(n) for n = 1..1000

Index entries for linear recurrences with constant coefficients, signature (9,-36,84,-126,126,-84,36,-9,1)

Formula

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.

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.

Prog

(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)

Crossrefs

Row 4 of A392417.

Sequence in context: A115203 A164547 A387034 * A298925 A016203 A241606

Adjacent sequences: A392417 A392418 A392419 * A392421 A392422 A392423

Keyword

nonn,easy

Author

Andrew Howroyd, Jan 13 2026

Status

approved