%I A131553
%S A131553 2,2,6,8,120,12,5040,384,12960,640,39916800,1152,6227020800,80640,
%T A131553 5443200,10321920,355687428096000,290304,121645100408832000,38707200,
%U A131553 384758035200,6812467200,25852016738884976640000,139345920
%N A131553 a(n) = product{1<=k<=n, GCD(k,n)=1} (1+k).
%H A131553 Leroy Quet, <a href="http://www.prism-of-spirals.net/">Home Page</a> 
               (listed in lieu of email address)
%e A131553 The positive integers which are <= 9 and are coprime to 9 are 1,2,4,5,
               7,8.
%e A131553 So a(9) = (1+1)(1+2)(1+4)(1+5)(1+7)(1+8) = 2*3*5*6*8*9 = 12960.
%p A131553 a:=proc(n) local p,k: p:=1: for k to n do if gcd(k,n)=1 then p:=p*(1+k) 
               else end if end do: p end proc: seq(a(n),n=1..22); - Emeric Deutsch 
               (deutsch(AT)duke.poly.edu), Sep 05 2007
%p A131553 for n to 25 do pr:=1: for k to n do if gcd(k,n)=1 then pr:=pr*(1+k) else 
               end if end do: a[n]:=pr end do: seq(a[n],n=1..25); - Emeric Deutsch 
               (deutsch(AT)duke.poly.edu), Aug 28 2007
%t A131553 Table[Times @@ (1 + Select[Range[n], GCD[ #, n] == 1 &]), {n, 1, 40}] 
               - Stefan Steinerberger (stefan.steinerberger(AT)gmail.com), Sep 14 
               2007
%o A131553 (PARI) rr(n) = pp=1;for(i=1,n,if(gcd(i,n)==1,pp=pp*(1+i)));return(pp); 
               for(j=1,60,print1(rr(j),",")) - Matthew M. Conroy, Sep 05 2007
%Y A131553 Sequence in context: A074933 A003178 A079494 this_sequence A094485 A021819 
               A000021
%Y A131553 Adjacent sequences: A131550 A131551 A131552 this_sequence A131554 A131555 
               A131556
%K A131553 nonn
%O A131553 1,1
%A A131553 Leroy Quet Aug 26 2007