This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A115111 #3 Mar 31 2012 13:21:02
%S A115111 0,0,0,256,5000,65880,739508,7653632,75687696,728589000,6899424840,
%T A115111 64678048600,602586261420,5593531747076,51815550195500,
%U A115111 479511147907328,4436081306716064,41044438822080816,379913227858140396
%N A115111 Number of different ways to select n elements from four sets of n elements under the precondition of choosing at least one element from each set.
%C A115111 The number of different ways to select n elements from four sets of n elements under the precondition of choosing at least one element from each set.
%F A115111 a(n) = binomial(4*n, n)-4*(binomial(3*n, n)+1)+6*binomial(2*n, n); also: a(n)=sum{binomial(n, i)*binomial(n, j)*binomial(n, k)*binomial(n, l)|i, j, k, l=1...(n-3), i+j+k+l=n}.
%e A115111 a(5)=binomial(20,5)-4*(binomial(15,5)+1)+6*binomial(10,5)=5000.
%Y A115111 Cf. A115246.
%K A115111 nonn
%O A115111 1,4
%A A115111 _Hieronymus Fischer_, Jan 22 2006