cp's OEIS Frontend

A137728 Second digit from the end of product of first n primes.

%I A137728 #10 Nov 22 2018 18:19:00
%S A137728 0,0,3,1,1,3,1,9,7,3,3,1,1,3,1,3,7,7,9,9,7,3,9,1,7,7,1,7,3,9,3,3,1,9,
%T A137728 1,1,7,1,7,1,9,9,9,7,9,1,1,3,1,9,7,3,3,3,1,3,7,7,9,9,7,1,7,7,1,7,7,9,
%U A137728 3,7,1,9,3,9,1,3,7,9,9,1,9,9,9,7,3,9,1,7,7,1,7,3,1,1,9,7,3,3,9,9,3,1,3,7,7
%N A137728 Second digit from the end of product of first n primes.
%C A137728 a(1) = a(2) = 0 because prime(1) = 2 and prime(1)*prime(2) = 6 are one-digit numbers.
%H A137728 Robert Israel, <a href="/A137728/b137728.txt">Table of n, a(n) for n = 1..10000</a>
%F A137728 a(n) = A002110(n)/10 mod 10 for n > 2; a(1) = a(2) = 0.
%p A137728 a[1]:= 0: a[2]:= 0: a[3]:= 3: p:= 5:
%p A137728 for n from 4 to 1000 do
%p A137728   p:= nextprime(p);
%p A137728   a[n]:= (a[n-1] * p) mod 10:
%p A137728 od: # _Robert Israel_, Nov 22 2018
%t A137728 a(1) = a(2) = 0, for n>2 Table[ Mod[ Product[ Prime[n], {n,1,k} ], 100 ]/10, {k,3,1000} ]
%Y A137728 Cf. A007652 = Final digit of prime(n).
%Y A137728 Cf. A110923 = Final two digits of prime(n).
%Y A137728 Cf. A137727 = Final digit of prime(n)*prime(n+1).
%Y A137728 Cf. A002110 = Primorial numbers, p#.
%K A137728 nonn,base
%O A137728 1,3
%A A137728 _Alexander Adamchuk_, Feb 08 2008