need help for function

[Max]

Directly in Pari code:

{ d2(n) = if(n%2,n!,n!-(n/2)!) }

{ a(n) = 2*n - 1 + sum(k=3,n,(n+1-k)*d2(k)) }

Max

Eugene McDonnell wrote:
> I have a sequence:
> 
> n 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
> a(n) 1 3 11 41 191 1055 6959 53159 462239 4499999 48454559 571409999 
> 7321386239 101249648639 1502852279039
> 
> where the second differences d2 are
> 
> n 3 4 5 6 7 8 9 10 11 12 13 14 15
> d2(n) 6 22 120 714 5040 40296 362880 3628680 39916800 479000880 
> 6227020800 87178286160 1307674368000
> 
> which have the property that odd and even d2(o) and d2(e) are o! and e! 
> - (e/2)!
> 
> How does one write a function that will generate sequence a?
> 
> Eugene McDonnell
> 
> 
>