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A158478
Number of colors needed to paint n sectors of a circle.
10
0, 1, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2
OFFSET
0,3
COMMENTS
No pair of adjacent sectors can have the same color.
For n > 0: smallest prime factor of A098548(n).
Decimal expansion of 61/4950. - Elmo R. Oliveira, May 05 2024
FORMULA
G.f.: x*(1+2*x+2*x^2)/(1-x^2).
E.g.f.: 2*cosh(x) + 3*sinh(x) - 2*(1 + x). - Stefano Spezia, Mar 24 2020
a(n) = a(n-2) for n > 3. - Elmo R. Oliveira, May 05 2024
a(n) = (n mod 2) + (2 mod (n+1)). - Aaron J Grech, Sep 02 2024
MATHEMATICA
Join[Range[0, 1], ConstantArray[{2, 3}, 20]] // Flatten (* Robert Price, Jun 15 2020 *)
PROG
(PARI) a(n)=if(n<4, n, 2+n%2)
(Haskell)
a158478 n = if n < 4 then n else 2 + mod n 2
a158478_list = [0..3] ++ cycle [2, 3]
-- Reinhard Zumkeller, Nov 30 2014
CROSSREFS
KEYWORD
nonn
AUTHOR
Jaume Oliver Lafont, Mar 20 2009
STATUS
approved