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A158411
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Maximum number of colors required to paint a map having n regions.
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6
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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; internal format)
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OFFSET
| 0,3
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COMMENTS
| The generating function can be arranged to have four zeros at the fourth roots of unity. [From Jaume Oliver Lafont (joliverlafont(AT)gmail.com), Mar 23 2009]
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LINKS
| Wikipedia, Four color theorem
Wolfram Mathworld, Four-Color Theorem
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FORMULA
| G.f.: x*(1+x+x^2+x^3)/(1-x)
G.f.: x*(1-x^4)/(1-x)^2 [From Jaume Oliver Lafont (joliverlafont(AT)gmail.com), Mar 20 2009]
G.f.: prod(k=0,3,1-I^k*x)*x/(1-x)^2 [From Jaume Oliver Lafont (joliverlafont(AT)gmail.com), Mar 23 2009]
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PROG
| (PARI) a(n)=if(n<4, n, 4)
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CROSSREFS
| Cf. A000934.
Cf. A130130. [From Jaume Oliver Lafont (joliverlafont(AT)gmail.com), Mar 20 2009]
a(n)=A130130(n)+A130130(n-2) [From Jaume Oliver Lafont (joliverlafont(AT)gmail.com), Mar 24 2009]
Sequence in context: A062750 A193669 A065686 * A065680 A093391 A029135
Adjacent sequences: A158408 A158409 A158410 * A158412 A158413 A158414
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KEYWORD
| nonn
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AUTHOR
| Jaume Oliver Lafont (joliverlafont(AT)gmail.com), Mar 18 2009
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