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Second digit from the end of product of first n primes.
2

%I #10 Nov 22 2018 18:19:00

%S 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 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 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 Second digit from the end of product of first n primes.

%C a(1) = a(2) = 0 because prime(1) = 2 and prime(1)*prime(2) = 6 are one-digit numbers.

%H Robert Israel, <a href="/A137728/b137728.txt">Table of n, a(n) for n = 1..10000</a>

%F a(n) = A002110(n)/10 mod 10 for n > 2; a(1) = a(2) = 0.

%p a[1]:= 0: a[2]:= 0: a[3]:= 3: p:= 5:

%p for n from 4 to 1000 do

%p p:= nextprime(p);

%p a[n]:= (a[n-1] * p) mod 10:

%p od: # _Robert Israel_, Nov 22 2018

%t a(1) = a(2) = 0, for n>2 Table[ Mod[ Product[ Prime[n], {n,1,k} ], 100 ]/10, {k,3,1000} ]

%Y Cf. A007652 = Final digit of prime(n).

%Y Cf. A110923 = Final two digits of prime(n).

%Y Cf. A137727 = Final digit of prime(n)*prime(n+1).

%Y Cf. A002110 = Primorial numbers, p#.

%K nonn,base

%O 1,3

%A _Alexander Adamchuk_, Feb 08 2008