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A131553 a(n) = Product_{k=1..n, gcd(k,n)=1} (1+k). 0

%I

%S 2,2,6,8,120,12,5040,384,12960,640,39916800,1152,6227020800,80640,

%T 5443200,10321920,355687428096000,290304,121645100408832000,38707200,

%U 384758035200,6812467200,25852016738884976640000,139345920

%N a(n) = Product_{k=1..n, gcd(k,n)=1} (1+k).

%e The positive integers that are <= 9 and are coprime to 9 are 1,2,4,5,7,8.

%e So a(9) = (1+1)(1+2)(1+4)(1+5)(1+7)(1+8) = 2*3*5*6*8*9 = 12960.

%p 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_, Sep 05 2007

%p 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_, Aug 28 2007

%t Table[Times @@ (1 + Select[Range[n], GCD[ #, n] == 1 &]), {n, 1, 40}] (* _Stefan Steinerberger_, Sep 14 2007 *)

%o (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 Conroy_, Sep 05 2007

%K nonn

%O 1,1

%A _Leroy Quet_, Aug 26 2007

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Last modified July 5 20:21 EDT 2020. Contains 335473 sequences. (Running on oeis4.)