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A138191
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Denominator of (n-1)n(n+1)/12.
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3
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1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| Proof of 4-periodicity follows from evaluating (n+3)(n+4)(n+5)/12, subtracting (n-1)n(n+1)/12 and getting n^2+4n+5 which is an integer. - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Mar 07 2008
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LINKS
| Eric Weisstein's World of Mathematics, KirchhoffIndex
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FORMULA
| a(n)=1+[A000292(n-1) mod 2] = a(n-4). O.g.f.: -1-5/[4(x-1)]+1/[4(x+1)]-1/[2(x^2+1)] . - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Mar 07 2008
a(n)=(1/24)*{5*(n mod 4)+5*[(n+1) mod 4]+11*[(n+2) mod 4]-[(n+3) mod 4]}, with n>=0 - Paolo P. Lava (paoloplava(AT)gmail.com), Mar 20 2008
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EXAMPLE
| 0, 1/2, 2, 5, 10, 35/2, 28, 42, 60, 165/2, 110, 143, 182, ...
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CROSSREFS
| Cf. A107453, A107453, A138190.
Sequence in context: A164115 A164117 A177704 * A069291 A081117 A129252
Adjacent sequences: A138188 A138189 A138190 * A138192 A138193 A138194
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KEYWORD
| nonn,frac,mult
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AUTHOR
| E. W. Weisstein (eric(AT)weisstein.com), Mar 04, 2008
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