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 A158411 Maximum number of colors required to paint a map having n regions. 8
 0, 1, 2, 3, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS The generating function can be arranged to have four zeros at the fourth roots of unity. - Jaume Oliver Lafont, Mar 23 2009 Also, the arithmetic function uhat(n,4,3) as defined in A291041. - Robert Price, Aug 25 2017 LINKS Wikipedia, Four color theorem Wolfram Mathworld, Four-Color Theorem FORMULA G.f.: x*(1+x+x^2+x^3)/(1-x). G.f.: x*(1-x^4)/(1-x)^2. - Jaume Oliver Lafont, Mar 20 2009 G.f.: prod(k=0,3,1-I^k*x)*x/(1-x)^2. - Jaume Oliver Lafont, Mar 23 2009 a(n) = A130130(n) + A130130(n-2). - Jaume Oliver Lafont, Mar 24 2009 a(n) = min(n,4). - Wesley Ivan Hurt, Apr 16 2014 PROG (PARI) a(n)=if(n<4, n, 4) CROSSREFS Cf. A000934, A291041. Cf. A130130. - Jaume Oliver Lafont, Mar 20 2009 Sequence in context: A062750 A193669 A065686 * A065680 A093391 A210964 Adjacent sequences:  A158408 A158409 A158410 * A158412 A158413 A158414 KEYWORD nonn,easy AUTHOR Jaume Oliver Lafont, Mar 18 2009 STATUS approved

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Last modified May 18 00:43 EDT 2021. Contains 343992 sequences. (Running on oeis4.)