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 A174371 a(n) = (6*n-1)^2. 3
 1, 25, 121, 289, 529, 841, 1225, 1681, 2209, 2809, 3481, 4225, 5041, 5929, 6889, 7921, 9025, 10201, 11449, 12769, 14161, 15625, 17161, 18769, 20449, 22201, 24025, 25921, 27889, 29929, 32041, 34225, 36481, 38809, 41209, 43681, 46225, 48841, 51529 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Unit together with numbers of form (6*n+5)^2. Sequence may be obtained by starting with the segment (1, 25) followed by the line from 25 in the direction 25, 121,... in the square spiral whose vertices are the generalized 20-gonal numbers. - Omar E. Pol, Jul 29 2016 LINKS Vincenzo Librandi, Table of n, a(n) for n = 0..1000 Index entries for linear recurrences with constant coefficients, signature (3,-3,1). FORMULA a(n) = A016970(n-1), n >= 1. G.f.: (49*x^2 + 22*x + 1)/(1 - x)^3. - Vincenzo Librandi, Jan 27 2013 a(n) = 6*A033579(n) + 1. - Miquel Cerda, Jul 28 2016 a(n) = 36n^2 - 12n + 1. - Omar E. Pol, Jul 28 2016 EXAMPLE a(0)=1 because (6*0-1)^2=1, a(1)=25 because (6*1-1)^2=25. MATHEMATICA CoefficientList[Series[(49*x^2 + 22*x + 1)/(1 - x)^3, {x, 0, 40}], x] (* Vincenzo Librandi, Jan 27 2013 *) PROG (MAGMA) [(6*n-1)^2: n in [0..50]]; // Vincenzo Librandi, May 07 2011 (PARI) a(n)=(6*n-1)^2 \\ Charles R Greathouse IV, Jul 28 2016 CROSSREFS Cf. A016970. Sequence in context: A213445 A031151 A016970 * A062938 A190875 A205800 Adjacent sequences:  A174368 A174369 A174370 * A174372 A174373 A174374 KEYWORD nonn,easy AUTHOR Juri-Stepan Gerasimov, Mar 17 2010 EXTENSIONS Offset and formula corrected by R. J. Mathar, Apr 16 2010 STATUS approved

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Last modified August 20 23:06 EDT 2018. Contains 313929 sequences. (Running on oeis4.)