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 A104249 a(n) = (3*n^2+n+2)/2. 14
 1, 3, 8, 16, 27, 41, 58, 78, 101, 127, 156, 188, 223, 261, 302, 346, 393, 443, 496, 552, 611, 673, 738, 806, 877, 951, 1028, 1108, 1191, 1277, 1366, 1458, 1553, 1651, 1752, 1856, 1963, 2073, 2186, 2302, 2421, 2543, 2668, 2796, 2927, 3061, 3198, 3338, 3481 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Second differences are all 3. Related to the sequence of odd numbers A005408 since for these numbers the first differences are all 2. Column 2 of A114202. - Paul Barry, Nov 17 2005 Equals third row of A167560 divided by 2. - Johannes W. Meijer, Nov 12 2009 A242357(a(n)) = n + 1. - Reinhard Zumkeller, May 11 2014 Also, this sequence is related to A011379, for n>0, by A011379(n) = n*a(n) - Sum_{i=0..n-1} a(i). - Bruno Berselli, Jul 08 2015 LINKS Vincenzo Librandi, Table of n, a(n) for n = 0..3000 Guo-Niu Han, Enumeration of Standard Puzzles Guo-Niu Han, Enumeration of Standard Puzzles [Cached copy] Index entries for linear recurrences with constant coefficients, signature (3,-3,1). FORMULA G.f.: (1+2*x^2)/(1-x)^3. Recurrence: {u(1) = 3, u(2) = 8, (n+3)*u(n+3)+(-5-n)*u(n+2)*(-2+2*n)*u(n+1) +(-2-2*n)*u(n), u(0) = 1}. a(0)=1, a(n) = a(n-1)+3n-1, n>0; a(n) = Sum_{k=0..n} C(n, k)C(2, k)J(k+1), J(n) = A001045(n). - Paul Barry, Nov 17 2005 Binomial transform of [1,2,3,0,...]. - Gary W. Adamson, Apr 23 2008 EXAMPLE The sequence of first differences delta_a(n) = a(n+1) - a(n) is: 2,5,8,11,14,17,20,23,26,... The sequence of second differences delta_delta_a(n) = a(n+2) - 2*a(n+1) + a(n) is: 3,3,3,3,3,3,3,3,3,... E.g. 78 - 2*58 + 41 = 3. MAPLE a := proc (n) local i, u; option remember; u := 1; u := 3; u := 8; for i from 3 to n do u[i] := -(4*u[i-3]-8*u[i-2]-2*u[i-1]+(-2*u[i-3]+2*u[i-2]-u[i-1])*i)/i end do; [seq(u[i], i = 0 .. n)] end proc; MATHEMATICA A104249[n_] := (3*n^2 + n + 2)/2; Table[A104249[n], {n, 0, 100}] (* Vladimir Joseph Stephan Orlovsky, Jul 22 2011 *) PROG (MAGMA) [(3*n^2+n+2)/2: n in [0..50]]; // Vincenzo Librandi, May 09 2011 (Haskell) a104249 n = n*(3*n+1) `div` 2 + 1 -- Reinhard Zumkeller, May 11 2014 (PARI) a(n)=n*(3*n+1)/2+1 \\ Charles R Greathouse IV, Oct 07 2015 CROSSREFS Cf. A001399, A002597, A005408, A011379, A016777, A143689. Sequence in context: A115006 A211480 A122796 * A225253 A254875 A025202 Adjacent sequences:  A104246 A104247 A104248 * A104250 A104251 A104252 KEYWORD nonn,easy AUTHOR Thomas Wieder, Feb 26 2005 STATUS approved

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Last modified January 22 13:41 EST 2020. Contains 331149 sequences. (Running on oeis4.)