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 A137879 Numbers k such that k^2 is a 17-gonal number. 4
 1, 133, 615, 64107, 296429, 30899441, 142878163, 14893466455, 68866978137, 7178619931869, 33193740583871, 3460079913694403, 15999314094447685, 1667751339780770377, 7711636199783200299, 803852685694417627311, 3716992648981408096433 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Corresponding 17-gonal numbers equal k^2 are listed in A137878. The 17-gonal numbers A051869(n) = n*(15n - 13)/2 are perfect squares for indices n listed in A137880. Note that all such indices are also perfect squares of numbers listed in A137881. LINKS Harvey P. Dale, Table of n, a(n) for n = 1..745 Index entries for linear recurrences with constant coefficients, signature (0,482,0,-1). FORMULA a(n) = sqrt(A137878(n)) = sqrt(A051869(A137880(n))) = sqrt(A051869(A137881(n)^2)). From Max Alekseyev, Oct 19 2008: (Start) For n>=5, a(n) = 482*a(n-2) - a(n-4). a(2n) = (-60 + 17*sqrt(30))/120 * (11 + 2*sqrt(30))^(2n) + (-60 - 17*sqrt(30))/120 * (11 - 2*sqrt(30))^(2n). a(2n+1) = (60 + 17*sqrt(30))/120 * (11 + 2*sqrt(30))^(2n) + (60 - 17*sqrt(30))/120 * (11 - 2*sqrt(30))^(2n). (End) MATHEMATICA LinearRecurrence[{0, 482, 0, -1}, {1, 133, 615, 64107}, 20] (* Harvey P. Dale, May 12 2014 *) PROG (PARI) is(n)=ispolygonal(n^2, 17) \\ Charles R Greathouse IV, Oct 16 2015 CROSSREFS Cf. A051869 (17-gonal numbers), A137878 (17-gonal numbers that are perfect squares), A137880, A137881. Sequence in context: A251131 A267288 A334037 * A249108 A020237 A217690 Adjacent sequences:  A137876 A137877 A137878 * A137880 A137881 A137882 KEYWORD nonn,easy AUTHOR Alexander Adamchuk, Feb 19 2008 EXTENSIONS Extended by Max Alekseyev, Oct 19 2008 STATUS approved

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Last modified October 16 20:36 EDT 2021. Contains 348047 sequences. (Running on oeis4.)