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 A138191 Denominator of (n-1)n(n+1)/12. 3
 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; text; internal format)
 OFFSET 1,2 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, Mar 07 2008 LINKS Eric Weisstein's World of Mathematics, KirchhoffIndex 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, 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, Mar 20 2008 EXAMPLE 0, 1/2, 2, 5, 10, 35/2, 28, 42, 60, 165/2, 110, 143, 182, ... CROSSREFS Cf. A107453, A107453, A138190. Sequence in context: A164115 A164117 A177704 * A069291 A081117 A129252 Adjacent sequences:  A138188 A138189 A138190 * A138192 A138193 A138194 KEYWORD nonn,frac,mult AUTHOR Eric W. Weisstein, Mar 04, 2008 STATUS approved

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