[lch]

Okay, the result isn't as great as I hoped, this is what Maple makes out of it: Code:

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> p := ((62-15*r+r*r)*5*n+70+3*r-r*r)/(2*6^(n+2));

                                                              2                  2

                                              5 (62 - 15 r + r ) n + 70 + 3 r - r

                                         p := ------------------------------------

                                                              (n + 2)

                                                           2 6

> factor(subs(r=r-1, p));

                                                                2               2

                                          390 n - 85 n r + 5 n r  + 66 + 5 r - r

                                          ---------------------------------------

                                                           (n + 2)

                                                        2 6

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