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A210487
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a(n) is the smallest possible greatest prime factor of prime(n)^2 - prime(k)^2 for 0 < k < n.
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2
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5, 2, 3, 3, 3, 5, 3, 5, 5, 3, 5, 3, 3, 5, 5, 3, 5, 3, 7, 3, 5, 3, 3, 5, 5, 5, 5, 3, 5, 5, 5, 5, 5, 5, 5, 7, 5, 5, 5, 5, 5, 7, 3, 5, 5, 7, 7, 5, 7, 5, 7, 5, 7, 5, 5, 5, 5, 5, 11, 3, 5, 3, 11, 5, 5, 5, 7, 5, 7, 5, 7, 7, 7, 7, 5, 5, 7, 5, 5, 7, 5, 7, 3, 5, 5, 5
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OFFSET
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2,1
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COMMENTS
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a(1) is not defined because there is no prime number smaller than 2.
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LINKS
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EXAMPLE
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n = 2, prime(2) = 3, 3^2 - prime(1)^2 = 5; so a(2) = 5;
n = 3, prime(3) = 5, 5^2 - prime(1)^2 = 21 = 3*7; 5^2 - prime(2)^2 = 16 = 2^4; Min(7, 2) = 2, so a(3) = 2.
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MAPLE
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local p, k, pk, a ;
a := ithprime(n)+ithprime(n-1) ;
p := ithprime(n) ;
for k from 1 to n-1 do
kp := ithprime(k) ;
a := min(a, %) ;
end do:
return a ;
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MATHEMATICA
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Table[Min[Table[Last[FactorInteger[Prime[i]^2 - Prime[j]^2]][[1]], {j, 1, i - 1}]], {i, 2, 87}]
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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