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A215906
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Even numbers n such that the Lucas number L(n) is the sum of two squares.
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3
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OFFSET
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1,2
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COMMENTS
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These Lucas numbers L(n) have no prime factor congruent to 3 mod 4 to an odd power.
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LINKS
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MATHEMATICA
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Select[Range[0, 200, 2], Length[FindInstance[x^2 + 1*y^2 == LucasL[#], {x, y}, Integers]] > 0 &] (* G. C. Greubel, Apr 14 2017 *)
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PROG
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(PARI) for(i=2, 500, a=factorint(fibonacci(i-1)+fibonacci(i+1))~; has=0; for(j=1, #a, if(a[1, j]%4==3&&a[2, j]%2==1, has=1; break)); if(has==0&&i%2==0, print(i", ")))
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CROSSREFS
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KEYWORD
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nonn,more
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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