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Number of sets which can be obtained by selecting unique elements from two sets with 2n and 3n elements respectively and n common elements.
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%I #7 Jun 17 2017 04:32:03

%S 6,23,51,90,140,201,273,356,450,555,671,798,936,1085,1245,1416,1598,

%T 1791,1995,2210,2436,2673,2921,3180,3450,3731,4023,4326,4640,4965,

%U 5301,5648,6006,6375,6755,7146,7548,7961,8385,8820,9266,9723,10191,10670

%N Number of sets which can be obtained by selecting unique elements from two sets with 2n and 3n elements respectively and n common elements.

%C Essentially identical to A022269. - R. J. Mathar, May 28 2008

%H <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (3,-3,1).

%F a(n)=(11*n^2+n)/2.

%F G.f.: x(6+5x)/(1-x)^3. - _R. J. Mathar_, Oct 23 2008

%e n=1: 2*n=2, 3*n=3, a(1)=6

%o (PARI) a(n)=(11*n^2+n)/2 \\ _Charles R Greathouse IV_, Jun 17 2017

%K nonn,easy

%O 1,1

%A Dolmatov S. (aalma(AT)mail.ru), Jun 24 2003