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A137727
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Final digit of prime(n)*prime(n+1).
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2
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6, 5, 5, 7, 3, 1, 3, 7, 7, 9, 7, 7, 3, 1, 1, 7, 9, 7, 7, 3, 7, 7, 7, 3, 7, 3, 1, 3, 7, 1, 7, 7, 3, 1, 9, 7, 1, 1, 1, 7, 9, 1, 3, 1, 3, 9, 3, 1, 3, 7, 7, 9, 1, 7, 1, 7, 9, 7, 7, 3, 9, 1, 7, 3, 1, 7, 7, 9, 3, 7, 7, 3, 1, 7, 7, 7, 3, 7, 9, 1, 9, 1, 3, 7, 7, 7, 3, 7, 3, 1, 3, 3, 7, 9, 7, 7, 9, 3, 3, 7, 9, 1, 7, 9, 7
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OFFSET
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1,1
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COMMENTS
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a(n) is 1, 3, 7, or 9 for n > 3. I conjecture that 1 and 9 appear 17/66 of the time and 3 and 7 appear 8/33 of the time. - Charles R Greathouse IV, Jan 03 2013
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LINKS
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FORMULA
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MATHEMATICA
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Table[ Mod[ Prime[n]*Prime[n+1], 10 ], {n, 1, 1000} ]
Mod[Times@@@Partition[Prime[Range[110]], 2, 1], 10] (* Harvey P. Dale, Oct 05 2014 *)
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PROG
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(Python)
from sympy import prime
def a(n): return (prime(n)*prime(n+1))%10
(Python) # much faster alternate for initial segment of sequence
from sympy import nextprime
def aupton(terms):
p1, p2, alst = 2, 3, []
while len(alst) < terms:
p1, p2, alst = p2, nextprime(p2), alst + [(p1*p2)%10]
return alst
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CROSSREFS
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Cf. A006094 (Products of 2 successive primes), A007652 (Final digit of prime(n)), A010879 (final digit of n), A110923 (final two digits of prime(n) (with leading zero omitted)), A137728 (second digit from the end of product of first n primes).
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KEYWORD
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nonn,base
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AUTHOR
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STATUS
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approved
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