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 A022268 a(n) = n*(11*n - 1)/2. 14
 0, 5, 21, 48, 86, 135, 195, 266, 348, 441, 545, 660, 786, 923, 1071, 1230, 1400, 1581, 1773, 1976, 2190, 2415, 2651, 2898, 3156, 3425, 3705, 3996, 4298, 4611, 4935, 5270, 5616, 5973, 6341, 6720, 7110, 7511, 7923, 8346, 8780, 9225, 9681, 10148, 10626, 11115 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Number of sets with two elements that can be obtained by selecting distinct elements from two sets with 2n and 3n elements respectively and n common elements. - Polina S. Dolmatova (polinasport(AT)mail.ru), Jul 11 2003 LINKS G. C. Greubel, Table of n, a(n) for n = 0..5000 Index entries for linear recurrences with constant coefficients, signature (3,-3,1). FORMULA G.f.: x*(5 + 6*x)/(1-x)^3. - Bruno Berselli, Feb 11 2011 a(n) = 11*n + a(n-1) - 6 for n>0. - Vincenzo Librandi, Aug 04 2010 a(n) = A000217(6*n-1) - A000217(5*n-1). - Bruno Berselli, Oct 17 2016 From Wesley Ivan Hurt, Dec 04 2016: (Start) a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3) for n > 2. a(n) = (1/9) * Sum_{i=n..10n-1} i. (End) E.g.f.: (1/2)*(11*x^2 + 10*x)*exp(x). - G. C. Greubel, Jul 17 2017 MAPLE A022268:=n->n*(11*n - 1)/2: seq(A022268(n), n=0..50); # Wesley Ivan Hurt, Dec 04 2016 MATHEMATICA Table[n (11 n - 1)/2, {n, 0, 40}] (* Bruno Berselli, Oct 14 2016 *) PROG (PARI) a(n)=n*(11*n-1)/2 \\ Charles R Greathouse IV, Sep 24 2015 (MAGMA) [n*(11*n - 1)/2 : n in [0..50]]; // Wesley Ivan Hurt, Dec 04 2016 CROSSREFS Cf. A000217, A022281. Cf. index to sequence with numbers of the form n*(d*n+10-d)/2 in A140090. Cf. similar sequences listed in A022288. Sequence in context: A146846 A296200 A041825 * A201279 A146721 A099979 Adjacent sequences:  A022265 A022266 A022267 * A022269 A022270 A022271 KEYWORD nonn,easy AUTHOR STATUS approved

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Last modified November 30 03:03 EST 2021. Contains 349416 sequences. (Running on oeis4.)