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
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
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
KEYWORD
nonn,easy
AUTHOR
STATUS
approved