OFFSET
1,1
COMMENTS
Previous name: "Smallest unrelated number belonging to a term of this sequence equals 8."
This is also the list of numbers n such that A259748(n)/n = 5/12. - José María Grau Ribas, Jul 12 2015.
Also the total number of line segments creating a stellated octahedron, where the length of each stellated edge equals n-1, and where the octahedron has 12 edges, each fixed at unit length. - Peter M. Chema, Apr 28 2016
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..3000
Tanya Khovanova, Recursive Sequences.
Index entries for linear recurrences with constant coefficients, signature (2,-1).
FORMULA
Min{URS[m]} = 8, where UNR[m] = Complement[RRS[m], Divisors[m]].
a(n) = 24*n - 12. - Max Alekseyev, Mar 03 2007
a(n) = 12*A005408(n-1). - Danny Rorabaugh, Oct 22 2015
G.f.: 12*x*(1 + x)/(1 - x)^2. - Ilya Gutkovskiy, Apr 28 2016
Sum_{n>=1} (-1)^(n+1)/a(n) = Pi/48. - Amiram Eldar, Feb 28 2023
EXAMPLE
URSet[12] = {8,9,10} so 12 is here.
MATHEMATICA
tn[x_] := Table[w, {w, 1, x}]; di[x_] := Divisors[x]; dr[x_] := Union[di[x], rrs[x]]; rrs[x_] := Flatten[Position[GCD[tn[x], x], 1]]; unr[x_] := Complement[tn[x], dr[x]]; Do[s=Min[unr[n]]; If[Equal[s, 8], Print[n]], {n, 1, 1000}]
Range[12, 2000, 24] (* Vladimir Joseph Stephan Orlovsky, Jun 14 2011 *)
PROG
(PARI) a(n)=24*n-12 \\ Charles R Greathouse IV, Jun 14 2011
(PARI) x='x+O('x^100); Vec(12*(1+x)/(1-x)^2) \\ Altug Alkan, Oct 22 2015
(Magma) [24*n-12: n in [1..60]]; // Vincenzo Librandi, Jun 15 2011
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Labos Elemer, Aug 08 2002
STATUS
approved