A180884 Number of permutations p() of 1..n+7 with centered difference p(i+1)-p(i-1) < 0 exactly 6 times

70, 4662, 203616, 5517204, 116189304, 1997701992, 29868078240, 398942612640, 4892905415970, 55931879316170, 604691896711760, 6237809698157180, 61935775158718032, 595207094582803248, 5567411131221296448

Offset

1,1

Comments

Column 7 of A180887

Links

R. H. Hardin, Table of n, a(n) for n=1..100

Prog

/* bc , formula r(n, k) from A000892 */
define factorial(n) {
auto prod;
prod=1;
while(n>=2)prod*=n--;
return prod;
}
define binomial(n, i) {
if(i<0||i>n)return 0;
return factorial(n)/(factorial(i)*factorial(n-i));
}
define r(n, k) {
auto j, sum;
sum=0;
for(j=0; j<=k+1; j++) {
sum+=(-1)^j*(k+1-j)^n*binomial(n+1, j);
}
return sum;
}
define t(n, k) {
auto sum, i;
sum=0;
for(i=0; i<=(k-1); i++)sum+=r((n+k)/2, i)*r((n+k)-(n+k)/2, (k-1)-i);
return sum*binomial((n+k), (n+k)/2);
}
for(n=1; n<=100; n++) {
print n, " ", t(n, 7), "\n";
}
quit

Crossrefs

Sequence in context: A258374 A363297 A146349 * A238540 A060057 A363296

Adjacent sequences: A180881 A180882 A180883 * A180885 A180886 A180887

Keyword

nonn

Author

R. H. Hardin Sep 23 2010

Status

approved