login
A137728
Second digit from the end of product of first n primes.
2
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, 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, 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
OFFSET
1,3
COMMENTS
a(1) = a(2) = 0 because prime(1) = 2 and prime(1)*prime(2) = 6 are one-digit numbers.
LINKS
FORMULA
a(n) = A002110(n)/10 mod 10 for n > 2; a(1) = a(2) = 0.
MAPLE
a[1]:= 0: a[2]:= 0: a[3]:= 3: p:= 5:
for n from 4 to 1000 do
p:= nextprime(p);
a[n]:= (a[n-1] * p) mod 10:
od: # Robert Israel, Nov 22 2018
MATHEMATICA
a(1) = a(2) = 0, for n>2 Table[ Mod[ Product[ Prime[n], {n, 1, k} ], 100 ]/10, {k, 3, 1000} ]
CROSSREFS
Cf. A007652 = Final digit of prime(n).
Cf. A110923 = Final two digits of prime(n).
Cf. A137727 = Final digit of prime(n)*prime(n+1).
Cf. A002110 = Primorial numbers, p#.
Sequence in context: A122506 A375286 A010274 * A054398 A093415 A233508
KEYWORD
nonn,base
AUTHOR
Alexander Adamchuk, Feb 08 2008
STATUS
approved