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 A188135 a(n) = 8*n^2 + 2*n + 1. 11
 1, 11, 37, 79, 137, 211, 301, 407, 529, 667, 821, 991, 1177, 1379, 1597, 1831, 2081, 2347, 2629, 2927, 3241, 3571, 3917, 4279, 4657, 5051, 5461, 5887, 6329, 6787, 7261, 7751, 8257, 8779, 9317, 9871, 10441, 11027, 11629, 12247, 12881 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Bisection of A193867. - Omar E. Pol, Aug 16 2011 Sequence found by reading the line from 1, in the direction 1, 11, ..., in the square spiral whose vertices are the triangular numbers A000217. - Omar E. Pol, Sep 04 2011 LINKS Index entries for linear recurrences with constant coefficients, signature (3,-3,1). FORMULA First differences: a(n) - a(n-1) = 16*n - 6 = A113770(n) = 2*A004770(n). Second differences: a(n) - 2*a(n-1) + a(n-2) = 16. a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3). From R. J. Mathar, Apr 06 2011: (Start) G.f.: -(1+x)*(7*x+1) / (x-1)^3. a(n) = A084849(2n). (End) PROG (MAGMA) [1 + 2*n + 8*n^2: n in [0..50]]; // Vincenzo Librandi, Mar 30 2011 (PARI) a(n)=8*n^2+2*n+1 \\ Charles R Greathouse IV, Oct 07 2015 CROSSREFS Cf. A185438. Sequence in context: A031381 A160023 A263201 * A188382 A090950 A217947 Adjacent sequences:  A188132 A188133 A188134 * A188136 A188137 A188138 KEYWORD nonn,easy AUTHOR Paul Curtz, Mar 30 2011 STATUS approved

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Last modified February 19 19:06 EST 2020. Contains 332047 sequences. (Running on oeis4.)