%I #11 Dec 03 2024 11:40:12

%S 1,2,6,3,1,1,3,1,9,7,3,3,1,1,3,1,3,7,7,9,9,7,3,9,1,7,7,1,7,3,9,3,3,1,

%T 9,1,1,7,1,7,1,9,9,9,7,9,1,1,3,1,9,7,3,3,3,1,3,7,7,9,9,7,1,7,7,1,7,7,

%U 9,3,7,1,9,3,9,1,3,7,9,9,1,9,9,9,7,3,9,1,7,7,1,7,3,1,1,9,7,3,3,9,9

%N Final nonzero digit of n-th primorial.

%C For n > 2, a(n) is in {1, 3, 7, 9}.

%H <a href="/index/Fi#final">Index entries for sequences related to final digits of numbers</a>

%F a(n) = prime(n)#/10 mod 10 for n > 2. - _Charles R Greathouse IV_, Dec 03 2024

%t Do[p = Product[Prime[m], {m, 1, n}]; While[Mod[p, 10] == 0, p = p/10]; Print[Mod[p, 10]], {n, 0, 100}]

%o (PARI) a(n)=if(n<3, return([1,2,6][n+1])); my(m=Mod(3,10)); forprime(p=7,prime(n), m*=p); lift(m) \\ _Charles R Greathouse IV_, Dec 03 2024

%Y Cf. A002110, A008904.

%K easy,nonn,base,changed

%O 0,2

%A _Robert G. Wilson v_, Jul 28 2000