OFFSET
1,5
COMMENTS
The number of different ways to select n elements from five sets of n elements under the precondition of choosing at least one element from each set.
FORMULA
a(n) = binomial(5*n,n)-5*binomial(4*n,n)+10*binomial(3*n,n)-10*binomial(2*n,n)+5; ; also: a(n)=sum{binomial(n,i)*binomial(n,j)*binomial(n,k)*binomial(n,l)*binomial(n,m)||i,j,k,l,m=1...(n-4),i+j+k+l+m=n}. General formula for N sets with m elements each: the number of different ways to select k elements from j different sets: G(N,m,j,k) = binomial(N,j)*sum(binomial(j,i)*binomial(i*m,k)*(-1)^i*(-1)^j|i=1...j); Recursion formula: G(N,m,j,k) = binomial(N,j)*binomial(j*m,k) - sum(binomial(N-i,j-i)*G(N,m,i,k)|i=1...j-1);
EXAMPLE
a(6)=binomial(30,6)-5*binomial(24,6)+10*binomial(18,6)-10*binomial(12,6)+5=97200;
MATHEMATICA
Table[Binomial[5n, n]-5Binomial[4n, n]+10Binomial[3n, n]-10Binomial[2n, n]+5, {n, 20}] (* Harvey P. Dale, Nov 06 2011 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Hieronymus Fischer, Jan 31 2006
STATUS
approved