A137728 Second digit from the end of product of first n primes.
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
Links
- Robert Israel, Table of n, a(n) for n = 1..10000
Crossrefs
Programs
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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
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Mathematica
a(1) = a(2) = 0, for n>2 Table[ Mod[ Product[ Prime[n], {n,1,k} ], 100 ]/10, {k,3,1000} ]
Formula
a(n) = A002110(n)/10 mod 10 for n > 2; a(1) = a(2) = 0.
Comments