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 A158478 Number of colors needed to paint n sectors of a circle. 9
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS No pair of adjacent sectors can have the same color. For n > 0: smallest prime factor of A098548(n). LINKS FORMULA G.f.: x*(1+2*x+2*x^2)/(1-x^2) a(n)=(5/2)-[(-1)^n]/2-2*[C(2*n,n) mod 2]-2*{C[(n+1)^2,n+3] mod 2}, with n>=0 [From Paolo P. Lava, Mar 31 2009] 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 Cf. A010693, A158411. Cf. A020639, A098548. Sequence in context: A307200 A165587 A010693 * A139713 A171465 A178620 Adjacent sequences:  A158475 A158476 A158477 * A158479 A158480 A158481 KEYWORD nonn AUTHOR Jaume Oliver Lafont, Mar 20 2009 STATUS approved

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Last modified May 24 00:38 EDT 2019. Contains 323528 sequences. (Running on oeis4.)