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 A051868 16-gonal (or hexadecagonal) numbers: a(n) = n*(7*n-6). 9
 0, 1, 16, 45, 88, 145, 216, 301, 400, 513, 640, 781, 936, 1105, 1288, 1485, 1696, 1921, 2160, 2413, 2680, 2961, 3256, 3565, 3888, 4225, 4576, 4941, 5320, 5713, 6120, 6541, 6976, 7425, 7888, 8365, 8856, 9361, 9880, 10413, 10960, 11521 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS Sequence found by reading the line from 0, in the direction 0, 16, ... and the parallel line from 1, in the direction 1, 45, ..., in the square spiral whose vertices are the generalized 16-gonal numbers. - Omar E. Pol, Jul 18 2012 This is also a star octagonal number: a(n) = A000567(n) + 8*A000217(n-1). - Luciano Ancora, Mar 29 2015 Let T(n) = A000217(n), the n-th triangular number. Then a(n) = T(n-1) + T(4n-3) - T(2n-4) + T(n-3).  In general, let P(k,n) be the n-th k-gonal number. Then for k>1, P(T(k)+1,n) = T(n-1) + T((k-1)n-(k-2)) - T((k-3)n-2(k-3)) + T((k-4)n-3(k-4)) - ... + (-1)^(k+1)*T(n-(k-2)). - Charlie Marion, Dec 23 2019 REFERENCES A. H. Beiler, Recreations in the Theory of Numbers, Dover, N.Y., 1964, p. 189. E. Deza and M. M. Deza, Figurate numbers, World Scientific Publishing (2012), page 6. LINKS Ivan Panchenko, Table of n, a(n) for n = 0..1000 Index entries for linear recurrences with constant coefficients, signature (3,-3,1). FORMULA a(n) = 14*n + a(n-1) - 13, with n>0, a(0)=0. - Vincenzo Librandi, Aug 06 2010 G.f.: x*(1+13*x)/(1-x)^3. - Bruno Berselli, Feb 04 2011 a(0)=0, a(1)=1, a(2)=16; for n>2, a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3). - Harvey P. Dale, May 07 2011 a(14*a(n) + 92*n + 1) = a(14*a(n) + 92*n) + a(14*n+1). - Vladimir Shevelev, Jan 24 2014 E.g.f.: exp(x)*x*(1 + 7*x). - Stefano Spezia, Dec 27 2019 a(n) = (4*n-3)^2 - (3*n-3)^2. In general, if we let P(k,n) be the n-th k-gonal number, then P(4k,n) = (k*n-k+1)^2 - ((k-1)*n-k+1)^2. In addition, {P(4k,n)} are the only polygonal number sequences each of whose terms can be written as the difference of two squares. - Charlie Marion, Feb 16 2020 MAPLE a[0]:=0:a[1]:=1:for n from 2 to 50 do a[n]:=2*a[n-1]-a[n-2]+14 od: seq(a[n], n=0..41); # Zerinvary Lajos, Feb 18 2008 MATHEMATICA s=0; lst={s}; Do[s+=n++ +1; AppendTo[lst, s], {n, 0, 6!, 14}]; lst (* Vladimir Joseph Stephan Orlovsky, Nov 16 2008 *) Table[n(7n-6), {n, 0, 50}] (* or *) LinearRecurrence[{3, -3, 1}, {0, 1, 16}, 51] (*  Harvey P. Dale, May 07 2011 *) PROG (PARI) a(n)=n*(7*n-6) \\ Charles R Greathouse IV, Jan 24 2014 CROSSREFS Cf. A000290, A000566, A051682, A051874, A255187, A282852. Sequence in context: A192143 A221593 A300962 * A209993 A322343 A318093 Adjacent sequences:  A051865 A051866 A051867 * A051869 A051870 A051871 KEYWORD nonn,easy AUTHOR N. J. A. Sloane, Dec 15 1999 STATUS approved

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Last modified October 21 23:47 EDT 2020. Contains 337948 sequences. (Running on oeis4.)