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Search: id:A130130
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| A130130 |
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a(0)=0, a(1)=1, a(n)=2 for n >= 2. |
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+0
4
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| 0, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2
(list; graph; listen)
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OFFSET
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0,3
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COMMENT
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a(n) = number of obvious divisors of n. The obvious divisors of n are the numbers 1 and n. [From Jaroslav Krizek (jaroslav.krizek(AT)atlas.cz), Mar 02 2009]
Number of colors needed to paint n adjacent segments on a line. [From Jaume Oliver Lafont (joliverlafont(AT)gmail.com), Mar 20 2009]
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FORMULA
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a(n)=2*[(n+2) mod (n+1)]-[n!^2 mod (n+1)]*[(n+1)!^2 mod (n+2)], with n>=0. - Paolo P. Lava (ppl(AT)spl.at), Aug 28 2007
G.f.: x*(1+x)/(1-x)=x*(1-x^2)/(1-x)^2 [From Jaume Oliver Lafont (joliverlafont(AT)gmail.com), Mar 20 2009]
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CROSSREFS
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Cf. A158411. [From Jaume Oliver Lafont (joliverlafont(AT)gmail.com), Mar 20 2009]
Sequence in context: A077433 A065685 A084100 this_sequence A046698 A036453 A040000
Adjacent sequences: A130127 A130128 A130129 this_sequence A130131 A130132 A130133
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KEYWORD
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nonn
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AUTHOR
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Paul Curtz (bpcrtz(AT)free.fr), Aug 01 2007
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