A391632 Number of mutual-visibility sets in the n-Andrásfai graph.

4, 21, 127, 749, 4455, 26725, 161007, 971613, 5866487, 35426517, 213940607, 1291991757, 7802356615, 47118492485, 284548794383

Offset

1,1

Links

Table of n, a(n) for n=1..15.

Eric Weisstein's World of Mathematics, Andrásfai Graph.

Eric Weisstein's World of Mathematics, Visibility Polynomial.

Formula

Conjectured g.f.: x*(4 - 19*x + 33*x^2 - 40*x^3 + 8*x^4)/(1 - 10*x + 29*x^2 - 32*x^3 + 8*x^4). - Andrew Howroyd, Jan 12 2026

Mathematica

Join[{4}, RootSum[8 - 32 # + 29 #^2 - 10 #^3 + #^4 &, #^Range[2, 15] (8 - 7 # + #^2) &]/4] (* Eric W. Weisstein, Feb 16 2026 *)
Join[{4}, Table[RootSum[8 - 32 # + 29 #^2 - 10 #^3 + #^4 &, 8 #^n - 7 #^(n + 1) + #^(n + 2) &]/4, {n, 2, 15}]] (* Eric W. Weisstein, Feb 16 2026 *)
ReplacePart[LinearRecurrence[{10, -29, 32, -8}, {3, 21, 127, 749}, 15], 1 -> 4] (* Eric W. Weisstein, Feb 16 2026 *)
CoefficientList[Series[(4 - 19 x + 33 x^2 - 40 x^3 + 8 x^4)/(1 - 10 x + 29 x^2 - 32 x^3 + 8 x^4), {x, 0, 14}], x] (* Eric W. Weisstein, Feb 16 2026 *)

Crossrefs

Sequence in context: A185047 A353608 A032326 * A281581 A007345 A255673

Adjacent sequences: A391629 A391630 A391631 * A391633 A391634 A391635

Keyword

nonn,more

Author

Eric W. Weisstein, Dec 14 2025

Extensions

a(10)-a(12) from Andrew Howroyd, Jan 12 2026

a(13)-a(15) from Andrew Howroyd, Jan 20 2026

Status

approved